Watershed-based Wetland Characterization for Delaware’s
Nanticoke River Watershed:
A Preliminary Assessment Report
U.S. Fish and Wildlife Service
National Wetlands Inventory
Northeast Region
Hadley, MA 01035
September 2001
Watershed-based Wetland Characterization for
Delaware’s Nanticoke River Watershed:
A Preliminary Assessment Report
by
R.W. Tiner, H.C. Bergquist, J.Q. Swords, and B.J. McClain
U.S. Fish and Wildlife Service
Northeast Region
National Wetlands Inventory Program
300 Westgate Center Drive
Hadley, MA 01035
Prepared for the
Delaware Department of Natural Resources and Environmental Control
Division of Soil and Water Conservation
89 Kings Highway
Dover, DE 19901
September 2001
This report should be cited as:
Tiner, R.W., H.C. Bergquist, J.Q. Swords, and B.J. McClain. 2001. Watershed-based Wetland
Characterization for Delaware’s Nanticoke River Watershed: A Preliminary Assessment Report.
U.S. Fish & Wildlife Service, National Wetlands Inventory (NWI) Program, Northeast Region,
Hadley, MA. Prepared for the Delaware Department of Natural Resources and Environmental
Control, Division of Soil and Water Conservation, Dover, DE. NWI technical report. 89 pp.
plus 22 maps.
Table of Contents
Page
Introduction 1
Study Area 1
Methods 2
Improved Baseline NWI Data 2
Expanded NWI Data 3
Preliminary Assessment of Wetland Functions 4
Wetland Restoration Site Inventory 6
Ditch Inventory 6
Water Resource Buffer Analysis 7
Overall Ecological Condition of the Watershed 8
General Scope and Limitations of the Study 14
Appropriate Use of this Report 18
Rationale for Preliminary Functional Assessments 19
Surface Water Detention 19
Streamflow Maintenance 20
Nutrient Transformation 20
Retention of Sediments and Other Particulates 23
Shoreline Stabilization 23
Provision of Fish and Shellfish Habitat 23
Provision of Waterfowl and Waterbird Habitat 25
Provision of Other Wildlife Habitat 26
Conservation of Biodiversity 29
Results 30
Wetland Classification and Inventory 30
Wetlands by NWI Types 30
Hydrogeomorphic-type Wetlands 33
Maps 36
Summary of Preliminary Assessment of Wetland Functions 37
Potential Wetland Restoration Sites 39
Extent of Ditching 41
Water Resource Buffer Analysis 41
Natural Habitat Integrity Indices 42
Values for the Entire Watershed 42
Summaries for Each Subbasin 43
Wildlife Travel Corridors 52
Conclusions 53
Acknowledgments 54
References 55
Appendices 59
1. Keys to Waterbody Type and Hydrogeomorphic-type Wetland
Descriptors for
for U.S. Waters and Wetlands (Operational Draft)
60
2. Preliminary Functional Assessment Findings for each Subbasin
83
Thematic Maps in separate folder on the CD
Introduction
Today there is great interest in managing wetland resources from a watershed standpoint or
landscape perspective. Wetland managers need information on a variety of topics including the
location and type of existing wetlands, wetland functions, potential wetland restoration sites, and
the overall condition of natural habitat in the watershed. The U.S. Fish and Wildlife Service’s
National Wetlands Inventory Program has developed products that expand the use of its
conventional maps and digital products to aid in resource management. The Delaware
Department of Natural Resources and Environmental Control (DNREC) is attempting to reduce
nonpoint source pollution impacts in the Nanticoke watershed and wanted the above information
for the Delaware portion of the Nanticoke River watershed. This information would be used to
help improve water quality and management and conservation of fish and wildlife habitat in
wetlands, streams, riparian areas, and uplands in Delaware. Similar work has recently been
completed for the Maryland portion of the watershed (Tiner et al. 2000). In the future, both
efforts may be combined into a single report.
The DNREC, through its Division of Soil and Water Conservation, provided funding to the
Service to produce watershed-wide information on wetlands, streams, riparian areas, and
uplands. The following products were scheduled for production: 1) a wetland characterization
report for the Delaware portion of the Nanticoke River watershed, 2) a set of GIS-produced maps
showing wetlands and highlighting wetlands of potential significance for performing various
functions, 3) edited and updated digital databases, 4) updated NWI maps for 11 quads, and 5) a
summary of the remotely-sensed natural habitat (ecological) integrity indices for the Nanticoke
River watershed and its subbasins.
The report is organized into the following sections: Study Area, Methods, General Scope and
Limitations of the Study, Appropriate Use of this Report, Rationale for Preliminary Functional
Assessments, Results, Conclusions, Acknowledgments, and References. Two appendices provide
keys to hydrogeomorphic wetland classification and the functional assessment findings for
subbasins. Thematic maps are contained in a separate folder on the CD version of this report.
Study Area
The study area is the Delaware portion of the Nanticoke River watershed. This roughly 490-
square mile drainage area occurs in western Delaware along its border with Maryland. It
represents about 25 percent of the state of Delaware. This watershed contains the six subbasins:
Broad Creek, Deep Creek, Gravelly Branch, Gum Branch, Marshyhope Creek, and the Nanticoke
River. The watershed encompasses parts of Sussex, Kent, and New Castle Counties. It appears
on the following 14 quads: Seaford West, Sharptown, Hebron, Hickman, Greenwood, Ellendale,
Seaford East, Georgetown, Laurel, Trap Pond, Delmar, Pittsville, Burrsville, and Harrington.
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Methods
The purpose of the project was to produce new information to assist Delaware wetland managers
in wetland planning and evaluation at the watershed level (see section on Appropriate Use of this
Report). The foundation of this project was construction of a fairly comprehensive, geospatial
wetland database. The existing wetland digital data for Delaware included the National
Wetlands Inventory (NWI) data (based on 1:24,000 maps derived from mostly early 1980s-1:58K
color infrared photography), the State’s wetland data (based on digital orthophoto quarter-quads
produced from spring 1992-1:40K color infrared photographs), and the State’s land use and land
cover data (mid-1990s data). The NWI data were used as the foundation since they are part of a
national database and match up well with other national digital data, especially hydrology data
from the U.S. Geological Survey. The State data were used as collateral data to improve the
delineation of wetlands in the NWI database. Updated NWI data and land use/land cover data
were derived through interpreting spring 1998-1:40K black and white photography.
The NWI database was also expanded to include hydrogeomorphic-type attributes for all mapped
wetlands and waterbodies, an inventory of ditches, an inventory of potential wetland restoration
sites, and geospatial data on land use and land cover in both watersheds. The information
contained within the database was then used to produce summary statistics, thematic maps, and a
wetland characterization report for the watersheds. The characterization included: 1) a summary
of the extent and distribution of wetland types (by NWI type and hydrogeomorphic type), 2) a
preliminary assessment of wetland functions for each watershed, 3) an inventory of potential
wetland restoration sites, 4) a description of the condition of wetland and waterbody buffers, 5)
an overall assessment of natural habitat for the watershed, and 6) an assessment of the extent of
ditching. The following discussion describes procedures used to produce this information. The
report summarizes the study findings for each watershed. These results should be considered
preliminary as they have not been subject to agency or field review.
Improved Baseline NWI Data
The first step in the project was updating the NWI maps and digital database, since these data
would be used for the analysis of wetland functions. The existing NWI dataset was both dated
(derived from early 1980s photography) and conservative (e.g., many flatwoods were not
mapped). We updated the NWI digital data using a digital transfer scope. This equipment
allowed integration of existing digital wetland and hydric soil data and editing of the digital data
through photointerpretation of spring 1998-1:40K black-and-white aerial photography. Digital
data used to assist in updating were: 1) Delaware wetlands produced by the State from 1992
photography, and 2) hydric soil data from the U.S.D.A. Natural Resources Conservation
Service’s (NRCS) soil surveys for Kent and Sussex Counties. Utilizing hydric soils digital data
to help expand the mapping of flatwood wetlands may have led to some errors of commission
(i.e., inclusion of upland forests in flatwood polygons), since these are among the most difficult
wetlands to photointerpret (Tiner 1999). These wetlands tended to be classified as a seasonally
saturated forested wetland of some kind (broad-leaved deciduous, needle-leaved evergreen, or
mixed; NWI codes such as PFO1B, PFO4B, PFO1/4B, and PFO4/1B). For the original NWI
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mapping, most of the mapped wet flatwoods were labelled as temporarily flooded, since ponding
was observed in a few places. Since the 1980s, more work has been done in the Coastal Plain
and the hydrology of wet flatwoods has been determined to be best described as “seasonally
saturated.” This is because high water tables are typical in winter and early spring, with little
standing water present. Locally these wetlands are often called “winter wet woods.” The
classifications of these flatwoods were revised to reflect a seasonally saturated condition (i.e.,
applied the “B” or “saturated” water regime modifier). The NRCS data for hydric soils and
Delaware wetland data were mainly used as collateral sources to aid in flatwood wetland
identification and the former also for assisting in classification of floodplain wetlands.
Expanded NWI Data
Once a more complete inventory of wetlands was created, the NWI database was further
expanded by adding hydrogeomorphic-type information to each mapped wetland. Landscape
position, landform, water flow path, and other descriptors were applied to all wetlands in the
NWI digital database by merging NWI data with on-line U.S. Geological Survey topographic
maps and consulting aerial photography where necessary (see Tiner 2000; Appendix of this
report for keys to these descriptors).
Landscape position defines the relationship between a wetland and an adjacent waterbody, if
present. Four landscape positions are relevant to the study watersheds: 1) lotic (along freshwater
rivers and streams), 2) lentic (in lakes, reservoirs, and their basins), 3) terrene (isolated,
headwater, or fragments of former isolated or headwater wetlands that are now connected to
downslope wetlands via drainage ditches), and 4) estuarine (in estuaries). Lotic wetlands are
further separated by river and stream gradients as high (e.g., shallow mountain streams on steep
slopes - not present in the study areas), middle (e.g., streams with moderate slopes - not present
in the study areas), low (e.g., mainstem rivers with considerable floodplain development as in the
Nanticoke watershed), and tidal (i.e., under the influence of the tides). "Rivers" are separated
from "streams" solely on the basis of channel width: watercourses mapped as linear (one-line)
features on an NWI map and a U.S. Geological Survey topographic map were designated as
streams, whereas two-lined channels (polygonal features) on these maps were classified as rivers.
Total river-stream length was determined by running a centerline through all river polygons and
adding this mileage to the miles of linear streams.
Landform is the physical form of a wetland or the predominant land mass on which it occurs
(e.g., floodplain or interfluve). Six types are recognized in the study areas: basin, interfluve, flat,
floodplain, fringe, and island (see Table 1 for definitions). The Johnston soil was the only soil
series in the watershed that was associated with floodplain wetlands.
Additional modifiers were assigned to indicate water flow paths associated with wetlands:
bidirectional, throughflow, inflow, outflow, or isolated. Bidirectional flow is two-way flow
either related to tidal influence or water level fluctuations in isolated lakes and impoundments.
Throughflow wetlands have either a watercourse or another type of wetland above and below it,
so water flows through the subject wetland. All lotic wetlands are throughflow types. Inflow
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wetlands are sinks where no outlets exist, yet water is entering via a stream or river or an upslope
wetland. Outflow wetlands have water leaving them and moving downstream via a watercourse
or a slope wetland. Isolated wetlands are essentially closed depressions or flats where water
comes from surface water runoff and/or ground water discharge.
Other descriptors applied to mapped wetlands include headwater, drainage-divide, and
fragmented. Headwater wetlands are sources of streams or wetlands along first order (perennial)
streams. They include wetlands connected to first order streams by ditches. The latter wetlands
were also labeled with a ditched modifier. Many such wetlands are remnants of once larger
interfluve wetlands that drained directly into streams. Drainage-divide wetlands are wetlands
that occur in more than one watershed or subbasin, straddling the defined watershed boundary
line between a watershed or subbasin and a neighboring one. We identified pieces of wetlands
separated by major highways (federal and state roads) as fragmented wetlands. This is a first step
in addressing the issue of fragmentation which is quite complex and beyond the scope of our
work. For example, we did not apply the descriptor to wetlands that were simply reduced in size
due to land use practices. The listing of fragmented wetlands is extremely conservative.
For open water habitats such as the ocean, estuaries, lakes, and ponds, we also applied additional
descriptors following Tiner (2000). For the study watersheds, such classification was mainly
relevant for ponds.
Preliminary Assessment of Wetland Functions
After improving and enhancing the NWI digital database, several analyses were performed to
produce a preliminary assessment of wetland functions for the watershed. Nine wetland
functions were evaluated: 1) surface water detention, 2) streamflow maintenance, 3) nutrient
transformation, 4) sediment and other particulate retention, 5) shoreline stabilization, 6) fish and
shellfish habitat, 7) waterfowl and waterbird habitat, 8) other wildlife habitat, and 9) biodiversity.
The rationale for correlating wetland characteristics with wetland functions is described in a
later section of this report. After running the analyses, a series of maps for watershed were
generated to highlight wetland types that may perform these functions at high or other significant
levels. Statistics and topical maps for the study area were generated by ArcView software.
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Table 1. Definitions and examples of landform types (Tiner 2000).
Landform Type General Definition Examples
Basin* a depressional (concave) landform lakefill bogs; wetlands in the
saddle between two
hills; wetlands in closed or
open depressions, including
narrow stream valleys
Slope a landform extending uphill (on a slope) seepage wetlands on
hillside; wetlands along
drainageways or mountain
streams on slopes
Flat* a relatively level landform, often on wetlands on flat areas
broad level landscapes with high seasonal ground-water
levels; wetlands on
terraces along rivers/streams;
wetlands on hillside benches;
wetlands at toes of slopes
Floodplain a broad, generally flat landform wetlands on alluvium;
occurring on a landscape shaped by bottomland swamps
fluvial or riverine processes
Interfluve a broad level to imperceptibly flatwood wetlands on coastal
depressional poorly drained landform or glaciolacustrine plains
occurring between two drainage systems
(on interstream divides)
Fringe a landform occurring along a flowing or buttonbush swamps; aquatic
standing waterbody (lake, river, stream) beds; semipermanently
and typically subject to permanent, flooded marshes; salt and
semipermanent flooding or frequent tidal brackish marshes
flooding; including wetlands within stream
or river channels and estuarine wetlands
with unrestricted tidal flow
Island a landform completely surrounded by deltaic and insular wetlands;
water (including deltas) floating bog islands
*May be applied as sub-landforms within the Interfluve and Floodplain landforms.
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Wetland Restoration Site Inventory
Wetland restoration efforts have been accelerating over the past decade throughout the country.
Much of the work done to date has been on an ad hoc basis without knowledge of a broader
universe of potential sites. In many areas of the country, site selection for wetland restoration has
simply been driven by opportunities and not by a holistic view of watersheds and wetland
resources. Recently, the State of Massachusetts initiated a watershed-based restoration process,
where potential wetland restoration sites are identified throughout an entire watershed, then
matched with locations of various “watershed-deficits” (e.g., flooding problems, areas of
degraded water quality, and lack of connectivity between significant fish and wildlife habitats) in
an effort to promote wetland restoration where the greatest public good can be gained. Such
work provides agencies, organizations, and others interested in wetland restoration with a wide
selection of potential sites. The Delaware Department of Natural Resources and Environmental
Control is interested in this process, so we identified potential wetland restoration sites for the
subject watershed.
An inventory of potential wetland restoration sites was performed by examining aerial photos,
hydric soil information, and existing wetland data (e.g., for farmed wetlands, wetlands
experiencing possible hydrologic restrictions, plus diked, ditched, and excavated vegetated
wetlands). Two major types of wetland restoration sites were identified: Type 1 sites - former
vegetated wetlands that appear suitable for restoration, and Type 2 sites - existing vegetated
wetlands whose functions appear to be significantly impaired by ditching, excavation, and
impoundment. Type 1 restoration sites included former wetlands that were filled and that did not
have buildings or other facilities constructed on them, farmed wetlands, and vegetated wetlands
that were converted to deepwater habitats such as impounded lakes. Farmed wetlands may
technically be considered Type 2 candidates, but since their condition is impaired to the point
that they only minimally meet the definition of wetland in the subject areas, they were considered
Type 1 sites. Type 2 restoration sites are mostly existing vegetated wetlands that are impounded,
excavated, partly drained (ditched), and potentially tidally restricted, but also include shallow
ponds constructed on hydric soils. For ditched wetlands, no attempt was made to evaluate the
scope and effect of ditching as this requires field-based assessment. One, however, might
consider the degree of ditching as observed on the map showing the extent of ditching as a way
of assessing the relative impact of ditching on various wetlands.
Ditch Inventory
To determine the extent of ditches in the watershed, we began with the digital hydrology
coverage from the U.S. Geological Survey 1:24K map series (digital line graphs - DLGs). This
coverage was reviewed to help separate “natural streams” from “ditches” and formed the
foundation for the “ditch” data layer. To create an up-to-date “ditch” coverage,
photointerpretation of 1998 aerial photography1 was performed using a digital transfer scope.
1For the Nanticoke watershed, initial mapping of ditches was accomplished by
photointerpreting 1989 photos since the 1998 photos were not available until later in the project.
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Ditches were separated from channelized and natural streams. Data presented include number of
ditch miles and the density of ditches per study watershed.
Water Resource Buffer Analysis
A 100m-wide (328 feet) stream buffer has been reported to be important for neotropical migrant
bird species in the Mid-Atlantic region (Keller et al. 1993) and streamside vegetation providing
canopy coverage over streams is important for lowering stream temperatures and moderating
daily fluctuations that is vital to providing suitable habitat for certain fish species (e.g., trout).
Review of the literature on buffers suggests wider buffers, such as 500m (1,640 feet) or more, for
certain species of wildlife (e.g., Kilgo et al. 1998 for southern bottomland hardwood stream
corridors). Semlitsch and Jensen (2001) emphasize that “wetland buffers” should be better
described as “core habitat” for semiaquatic species and they urge that such areas be protected and
managed as vital habitats. They found that 95 percent of the breeding population of mole
salamanders lived in the adjacent forest within 164m (538 feet) of their vernal pool wetland. An
interesting article by Finlay and Houlahan (1996) indicates that land use practices around
wetlands may be as important to wildlife as the size of the wetland itself. They reported that
removing 20 percent of the forest within 1000m (3,281 feet) of a wetland may have the same
effect on species as destroying 50 percent of the wetland. For literature reviews of wetland and
stream buffers, see Castelle et al. (1994) and Desbonnet et al. (1994).
The condition of these buffers is also significant for locating possible sources of water quality
degradation. Wooded corridors should provide the best protection, while developed corridors
(e.g., urban or agriculture) should contribute to substantial water quality and aquatic habitat
deterioration. Since wetland and waterbody buffers are important features that relate to the
quality of these aquatic habitats, we performed an analysis of the condition of these buffers. This
information was also used in evaluating the overall ecological condition or the condition of
natural habitats for each watershed.
These data were updated with the 1998 photos to create a 1998-era database for ditches.
A 100m-wide buffer was selected for analysis. The buffer was positioned around various water
resource features, i.e., wetlands, lakes, ponds, streams, and ditches. To evaluate the condition of
the buffer, we created a land use/land cover data layer by combining existing digital data with
new photointerpretation. The state’s existing digital data on land use/land cover was used as the
foundation. These data were updated by interpreting 1998 aerial photography (1:40,000 black
and white) using a digital transfer scope. We used the Anderson et al. (1976) land use/land cover
classification system and classified upland habitats to level two in this system. The following
categories were among those identified: developed land (e.g., residential, commercial, industrial,
transportation/communication, utilities, other, institutional/government, and recreational),
agricultural land (cropland, pasture, orchards, nurseries, horticulture, feedlots, and holding areas),
forests (deciduous, evergreen, mixed, and clear-cut), wetlands (from NWI data), and transitional
8
land (moving toward some type of development or agricultural use, but future status unknown).
Data layers were constructed for the entire “land” area of each watershed so that information
could also be used for assessing their overall ecological condition. Buffer analysis is one of the
key landscape variables used to judge this condition. Data on buffers were reported for various
water resource features: perennial nontidal rivers and streams, wetlands, ponds and lakes
(impoundments), and a few combinations of perennial rivers and streams, intermittent streams,
and ditches.
Overall Ecological Condition of the Watershed
There are many ways to assess land use/cover changes and habitat disturbances. The health and
ecological condition of a watershed may be assessed by considering such features as the integrity
of the lotic wetlands and riparian forests (upland forests along streams), the percent of land uses
that may adversely affect water quality in the watershed (% urban, % agriculture, % mining, etc.),
the actual water quality, the percent of forest in the watershed, and the number of dams on
streams, for example. Recent work on assessing the condition of watersheds has been done in
the Pacific Northwest to address concerns for salmon (Wissmar et al. 1994; Naiman et al. 1992).
A Wisconsin study by Wang et al. (1997) found that instream habitat quality declined when
agricultural land use in a watershed exceeded 50 percent, while when only 10-20 percent of the
watershed was urbanized, severe degradation occurred.
To assess the overall ecological condition of watersheds, the Northeast Region of the U.S. Fish
and Wildlife Service has developed a set of largely remotely-sensed “natural habitat integrity”
indices (formerly referred to as “ecological integrity indices”). The variables for these indices are
derived through air photointerpretation and/or satellite image processing coupled with knowledge
of the historical extent of wetlands and open waterbodies. They are coarse-filter variables for
assessing the overall condition of watersheds. They are intended to augment, not supplant, other
more rigorous, fine-filter approaches for describing the ecological condition of watersheds (e.g.,
indices of biological integrity for macroinvertebrates and fish and the extent and distribution of
invasive species) and for examining relationships between human impacts and the natural world.
The natural habitat integrity indices can be used to develop “habitat condition profiles” for
individual watersheds of varying scales (i.e., subbasins to major watersheds). Indices can be
used for comparative analysis of subbasins within watersheds and to compare one watershed with
another. They may also serve as one set of statistics for reporting on the “state-of-the-environment”
by government agencies and environmental organizations or for evaluating the
historic trends in the extent of natural habitats.
The indices are rapid-assessment types that allow for frequent updating (e.g., every 5-10 years).
They may be used to assess and monitor the amount of “natural habitat” compared to the amount
of disturbed aquatic habitat (e.g., channelized streams, partly drained wetlands, and impounded
wetlands) or developed habitat (e.g., cropland, grazed meadows, mined lands, suburban
development, and urbanized land). The index variables include features important to natural
resource managers attempting to lessen the impact of human development on the environment.
The indices may also be compared with other environmental quality metrics such as indices of
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biological integrity for fish and/or macroinvertebrates or water quality parameters. If significant
correlations can be found, they may aid in projecting a “carrying capacity” or threshold for
development for individual subbasins. This would require further classification of the developed
land category into various agricultural types and urban/suburban types which is easily
accomplished.
Prior to initiating this project, a total of nine indices were developed for nontidal areas. We split
one of them into two indices for a new total of ten indices. All of them, in one way or another,
represent habitat condition in a watershed. Six indices address natural habitat extent (i.e., the
amount of natural habitat occurring in the watershed and along wetlands and waterbodies):
natural cover, river-stream corridor integrity, vegetated wetland buffer integrity, pond and lake
buffer integrity, wetland extent, and standing waterbody extent. Use of terms like “natural
habitat” and “natural vegetation” have stirred much debate, yet despite this, we feel that they are
useful for discussing the effects of human activities on the environment. For purposes of this
study, “natural habitats” are defined as areas where significant human activity is limited to nature
observation, hunting, fishing, or timber harvest, and where vegetation is allowed to grow for
many years without annual introduction of chemicals or annual harvesting of vegetation or fruits
and berries for commercial purposes. Natural habitats may be managed, yet are not intensively
managed or subjected to heavy human traffic. They are places where wetland and terrestrial
wildlife find food, shelter, and water. In other words, they are essentially plant communities
represented by “natural” vegetation such as forests, meadows, and shrub thickets. They are not
developed sites (e.g., impervious surfaces, lawns, turf, cropland, pastures, or mowed hayfields).
Managed forests are included as natural habitat, whereas orchards and vineyards are not.
“Natural habitat” therefore includes habitats ranging from pristine woodlands and wetlands to
wetlands now colonized by invasive species (e.g., Phragmites australis or Lythrum salicaria) or
commercial forests planted with loblolly pine. Natural vegetation does not imply that substantial
groundcover must be present, but simply that the communities reflect the vegetation that is
capable of growth and reproduction in accordance with site characteristics (e.g., sand dunes and
beaches).
Three indices emphasize human-induced alterations to streams and wetlands. These “stream and
wetland disturbance indices” address dammed stream flowage, channelized stream flowage, and
wetland disturbance. The nine specific indices may be combined into a single, composite index
called “remotely-sensed natural habitat integrity index” for the watershed. All indices have a
maximum value of 1.0 and a minimum value of zero. For the habitat extent indices, the higher
the value, the more habitat available. For the disturbance indices, the higher the value, the more
disturbance. For the remotely-sensed natural habitat integrity index, all indices are weighted,
with the disturbance indices subtracted from the habitat extent indices to yield an overall “natural
habitat integrity” score for the watershed.
Data for these indices came from the improved NWI digital database and a newly created land
use/land cover database for the two watersheds. The data were derived primarily through aerial
photointerpretation with review of existing information. The indices do not include certain
qualitative information on the condition of the existing habitats (habitat quality) as reflected by
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the presence, absence, or abundance of invasive species or by fragmentation of forests, for
example. It may be possible to add such data in the future, especially for the latter. Another
consideration would be establishment of minimum size thresholds to determine what constitutes
a viable “natural habitat” for analysis (e.g., 0.04 hectare/0.1 acre patch of forest or 0.4 hectare/1
acre minimum?). Other indices may also need to be developed to aid in water quality
assessments (e.g., index of ditching density for agricultural and silvicultural lands). The nine
indices are summarized below.
Habitat Extent Indices
These indices have been developed to provide some perspective on the amount of natural
vegetation that occurs in a watershed. The following areas are emphasized: the entire watershed,
stream and river corridors, vegetated wetlands and their buffers, and pond and lake buffers. The
extent of standing waterbodies is also included to provide information on the amount of aquatic
habitat in the watershed. Each index is briefly described below.
The Natural Cover Index (INC) is derived from a simple percentage of the subbasin that is
wooded (e.g., upland forests or shrub thickets and forested or scrub-shrub wetlands) and
“natural” open land (e.g., emergent wetlands or “old fields;” but not cropland, hayfields, lawns,
turf, or pastures). These areas are lands supporting “natural vegetation” and they exclude open
water of ponds, rivers, lakes, streams, and coastal bays.
INC = ANV/AW , where ANV (area in natural vegetation) equals the area of the watershed’s
land surface in “natural” vegetation and AW is the area of "watershed" excluding open
water.
The River-Stream Corridor Integrity Index (IRSCI) is derived by considering the condition of the
stream corridors around perennial rivers and streams2:
IRSCI = AVC/ATC , where AVC (vegetated river-stream corridor area) is the area of the
river-stream corridor that is colonized by “natural vegetation” and ATC (total river-stream
corridor area) is the total area of the river-stream corridor.
2Including streams designated as seasonally flooded/saturated intermittent streams (i.e.,
R4SBEx) which flow for long periods during the year, but not year-round. Such streams were
identified on the source data (U.S.Geological Survey DLGs) as perennial, but based on our field
experiences and those of Amy Jacobs (DNREC) it was agreed that these streams are not
perennial.
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The width of the river-stream corridor may be varied to suit project goals, but for this project, a
200-meter (656 feet) corridor (100m on each side of the river or stream) was evaluated. To
compute total river-stream length, the centerlines of river polygons are used to derive river length
and this was added to stream length (from linear data). Also note that these corridors include
impounded sections of rivers and streams, so that a continuous river or stream corridor is
evaluated. The centerlines of these polygons were used to determine stream length. For this
watershed, the index was applied to nontidal rivers for assessing the composite natural habitat
integrity index. When the entire Nanticoke River watershed is evaluated in the future, the index
should include tidal portions of the river as well.
The Wetland Buffer Integrity Index (IWB) is a measure of the condition of wetland buffers within
a specified distance (e.g., 100m) of mapped vegetated wetlands for the entire watershed:
IWB = AVB/ATB , where AVB (area of vegetated buffer) is the area of the buffer zone that is
in natural vegetation cover and ATB is the total area of the buffer zone.
This buffer is drawn around existing vegetated wetlands. While the buffer zone may include
open water, the buffer index will focus on land areas that may support free-standing vegetation.
Note that for the analysis of the Maryland portion of the Nanticoke River watershed, the wetland
buffers were included with the pond and lake buffers in an index called Wetland and Waterbody
Buffer Index (IWWB). Buffer width can be varied according to regional needs and conditions. For
the Nanticoke River watershed analysis, a 100m buffer was examined.
The Pond and Lake Buffer Integrity Index (IPLB) addresses the status of buffers of a specified
width around these standing waterbodies (excluding in-stream impoundments that are included in
the river-stream corridor integrity index):
IPLB = AVB/ATB , where AVB (area of vegetated buffer) is the area of the buffer zone that
is in natural vegetation cover and ATB is the total area of the buffer zone.
See comments under the wetland buffer integrity index above. Ponds are shallow waterbodies
mapped as palustrine unconsolidated bottoms and unconsolidated shores by NWI. Vegetated
ponds are mapped as a vegetated wetland type and their buffers are not included in this analysis,
but instead are evaluated as wetland buffers. For the Nanticoke River watershed analysis, a
100m buffer was examined.
The Wetland Extent Index (IWE) compares the current extent of vegetated wetlands (excluding
nonvegetated, open-water wetlands) to the estimated historic extent.
IWE = ACW/AHW , where ACW is the current area of vegetated wetland in the watershed
and AHW is the historic vegetated wetland area in the watershed.
12
The IWE is an approximation of the extent of the original wetland acreage remaining in the
watershed. Farmed wetlands are included where cultivation is during droughts only, since they
are likely to support “natural vegetation” during normal and wet years. Where farmed wetlands
are cultivated more or less annually such as in much of the Northeast region, they are not
included in the area of vegetated wetland, since they lack “natural vegetation” in most years and
only minimally function as wetland. For the Nanticoke watershed, hydric soils data are available
for the Kent and Sussex Counties portion of the watershed and were used to calculate the wetland
extent index for the watershed.
The Standing Waterbody Extent Index (ISWE) addresses the current extent of standing fresh
waterbodies (e.g., lakes, reservoirs, and open-water wetlands - ponds) in a watershed relative to
the historic area of such features.
ISWE = ACSW/AHSW , where ACSW is the current standing waterbody area and AHSW is the
historic standing waterbody area in the watershed.
Since the Nanticoke watershed has experienced a net gain in ponds and impoundments over time,
the ISWE value is 1.0+ which indicates a gain in this aquatic resource with no specific calculations
necessary. A value of 1.0 was used for determining the composite natural habitat integrity index
for the watershed.
Stream and Wetland Disturbance Indices
A set of three indices have been developed to address alterations to streams and wetlands. For
these indices, a value of 1.0 is assigned when all of the streams or existing wetlands have been
modified.
The Dammed Stream Flowage Index (IDSF) highlights the direct impact of damming on rivers and
streams in a watershed.
IDSF = LDS/LTS , where LDS is the length of perennial streams impounded by dams
(combined pool length) and LTS is the total length of perennial streams in the watershed
(including the length of in-stream pools).
Note that the total stream length used for this index will be greater than that used in the
channelized stream length index, since the latter emphasizes existing streams and excludes the
length of dammed segments. See footnote 2. Also note that this index was not applied to the full
length of the Nanticoke River, but only to linear streams. In the future, this index should be
expanded to include the entire river-stream length (i.e., the Dammed River-Stream Flowage
Index).
The Channelized Stream Length Index (ICSL) is a measure of the extent of channelization of
streams within a watershed.
13
ICSL = LCS/LTS , where LCS is the channelized stream length and LTS is the total stream
length for the watershed.
Since this index addresses channelization of existing streams, it focuses on the linear streams.
The index will usually emphasize perennial streams as it does for the Nanticoke River study, but
could include intermittent streams, if desirable. See footnote 2. The total stream length does not
include the length of: 1) artificial ditches excavated in farmfields and forests, 2) dammed
sections of streams, and 3) polygonal portions of rivers.
The Wetland Disturbance Index (IWD) focuses on alterations within existing wetlands. As such,
it is a measure of the extent of existing wetlands that are diked/impounded, ditched, excavated,
or farmed:
IWD = ADW/ATW , where ADW is the area of disturbed or altered wetlands and ATW is the
total wetland area in the watershed.
Wetlands are represented by both vegetated and nonvegetated (e.g., shallow ponds) types and
also include natural and created wetlands. Since the focus of our analysis is on “natural habitat,”
diked or excavated wetlands (or portions thereof) are viewed as an adverse action. We
recognize, however, that many such wetlands may serve as valuable wildlife habitats (e.g.,
waterfowl impoundments), yet they remain classified as disturbed wetlands.
Composite Habitat Index for the Watershed
The Composite Natural Habitat Integrity Index (ICNHI) is a combination of the preceding indices.
It seeks to express the overall condition of a watershed in terms of its potential ecological
integrity or the relative intactness of “natural” plant communities and waterbodies, without
reference to specific qualitative differences among these communities and waters. Variations of
ICNHI may be derived by considering buffer zones of different widths around wetlands and other
aquatic habitats (e.g., ICNHI 100 or ICNHI 200) and by applying different weights to individual indices
or by separating or aggregating various indices (e.g., stream corridor integrity index, river
corridor integrity index, or river-stream corridor integrity index).
For the analysis of Delaware’s Nanticoke River watershed, the following formula was used to
determine this composite index:
ICNHI 100 = (0.5 x INC) + (0.125 x IRSCI200) + (0.125 x IWB100) + (0.05 x IPLB100)+ (0.1 x IWE), + (0.1 x
ISWE) - (0.1 x IDSF) - (0.1 x ICSL) - (0.1 x IWD)
where the condition of the 100m buffer is used throughout. (Note: With this size buffer, the
river/stream corridor width becomes 200m.)
While the weighting of the indices may be debatable, the results of this analysis are comparable
among subbasins. The same weighting scheme must be used whenever comparisons of this
index are made between watersheds or major portions of watersheds, such as the Maryland
portion of the Nanticoke to the Delaware portion of the Nanticoke watershed.3
Data for Natural Habitat Integrity Indices
The data used to compile these indices come from a few sources. Primary data sources included
the enhanced NWI digital data layer, U.S.D.A. Natural Resources Conservation Service’s soil
data, the State’s land use/land cover data for the Nanticoke watershed. and the U.S. Geological
Survey digital line graphs (DLGs). We updated the original NWI data to the year 1998 through
photointerpretation using a digital transfer scope. Spring 1998-1:40,000 black and white
photography was used for updating. This update focused on major areas of land use change and,
therefore, does not represent a comprehensive revision. We emphasized changes between
“natural” habitat, agriculture, and developed land. We added coding for larger levees along
channelized streams, but did not recode all levees. Many levees had been classified as
agricultural land by the State. Stream data based on 1:24,000 topographic maps were expanded
to include a more complete assessment of ditches and channelized stream segments. We also
changed the classification of many headwater stream segments draining interfluve wetlands from
perennial to intermittent (seasonally flooded/saturated = “E”) since such streams do not flow
year-round (confirmed by Amy Jacobs, Delaware Department of Natural Resources and
Environmental Control)
General Scope and Limitations of the Study
Wetland Inventory and Digital Database
The wetlands inventory and digital database are an update of the original NWI database and serve
as the foundation for a preliminary watershed characterization. One must, however, recognize
the limitations of any wetland mapping effort derived mainly through photointerpretation
techniques (see Tiner 1997, 1999 for details). For example, use of spring aerial photography for
wetland mapping precludes identification of freshwater aquatic beds. Such areas are included
within areas mapped as open water (e.g, lacustrine and palustrine unconsolidated bottom)
because vegetation is not developed so they appear as water on the aerial photographs. Also
drier-end wetlands such as seasonally saturated and temporarily flooded wetlands are often
difficult to separate from nonwetlands through photointerpretation.
3For the Maryland portion of the Nanticoke watershed, an earlier version of the formula was
used, so results are not equivalent, although they should be similar. Additional analysis is
required to make more valid comparisons.
14
Although not a prime purpose of the study, we identified some wetlands that were subjected to
fragmentation. Our approach was an extremely conservative one, focusing on wetlands separated
by major roads. We recognize that many small wetlands are actually the remaining fragments
(remnants) of once large wetlands and may also be considered fragments. However, for this
15
report, we applied the fragmented descriptor ("fg") only to wetlands that were divided into two or
more units by major roads which likely disrupted the hydrology and created an increased risk for
wildlife crossing. Moreover, the fragmented descriptor was only applied to pieces of wetlands
separated by major roads, hence the results are extremely conservative. Fragmentation in this
context, therefore, did not address the issue from the broad landscape perspective. To do so
requires analysis beyond the scope of our study. For readers with an interest in fragmentation,
the overall pattern of habitat fragmentation can be seen by looking at Map 22, while the pattern
of wetland fragmentation may be observed on one of the wetland maps prepared for this study
(i.e., Maps 1-4).
Preliminary Assessment of Wetland Functions
At the outset, it is important to emphasize that this functional assessment is a preliminary one
based on wetland characteristics interpreted through remote sensing and using the best
professional judgment of the senior author and an ad hoc group of wetland specialists assembled
by the DNREC.4 Wetlands believed to be providing potentially high or other significant levels of
performance for a particular function were highlighted. As the focus of this report is on
wetlands, an assessment of deepwater habitats (e.g., lakes, rivers, and estuaries) for providing the
listed functions was not done (e.g., it is rather obvious that such areas provide significant
functions like fish habitat). Also, no attempt was made to produce a more qualitative ranking for
each function or for each wetland based on multiple functions as this would require more input
from others and more data, well beyond the scope of this study. For a technical review of
wetland functions, see Mitsch and Gosselink (2000) and for a broad overview, see Tiner (1985;
1998).
4On June 14, 2001, DNREC held a workshop to review draft protocols prepared by the U.S.
Fish and Wildlife Service for this project based on previous wetland assessment studies including
one for the Maryland portion of the Nanticoke watershed. Fourteen participants included
representatives from DNREC, Delaware Natural Heritage Program, Maryland Department of
Natural Resources, Maryland Department of the Environment, Smithsonian Environmental
Research Center, and U.S. Geological Survey (see Acknowledgments).
Functional assessment of wetlands can involve many parameters. Typically such assessments
have been done in the field on a case-by-case basis, considering observed features relative to
those required to perform certain functions or by actual measurement of performance. The
present study does not seek to replace the need for such evaluations as they are the ultimate
assessment of the functions for individual wetlands. Yet, for a watershed analysis, basin-wide
16
field-based assessments are not practical or cost-effective or even possible given access
considerations. For watershed planning purposes, a more generalized assessment is worthwhile
for targeting wetlands that may provide certain functions, especially for those functions
dependent on landscape position and vegetation life form. Subsequently, these results can be
field-verified when it comes to actually evaluating particular wetlands for acquisition purposes,
e.g., for conservation of biodiversity or for preserving flood storage capacity. Current aerial
photography may also be examined to aid in further evaluations (e.g., condition of
wetland/stream buffers or adjacent land use) that can supplement our preliminary assessment.
This study employs a watershed assessment approach that may be called "Watershed-based
Preliminary Assessment of Wetland Functions" (W-PAWF). W-PAWF applies general
knowledge about wetlands and their functions to develop a watershed overview that highlights
possible wetlands of significance in terms of performance of various functions. To accomplish
this objective, the relationships between wetlands and various functions must be simplified into a
set of practical criteria or observable characteristics. Such assessments could also be further
expanded to consider the condition of the associated waterbody and the neighboring upland or to
evaluate the opportunity a wetland has to perform a particular function or service to society, for
example.
W-PAWF usually does not account for the opportunity that a wetland has to provide a function
resulting from a certain land-use practice upstream or the presence of certain structures or land-uses
downstream. For example, two wetlands of equal size and like vegetation may be in the
right landscape position to retain sediments. One, however, may be downstream of a land-clearing
operation that has generated considerable suspended sediments in the water column,
while the other is downstream from an undisturbed forest. The former should be actively
performing sediment trapping in a major way, while the latter is not. Yet if land-clearing takes
place in the latter area, the second wetland will likely trap sediments as well as the first wetland.
The entire analysis typically tends to ignore opportunity since such opportunity may occurred in
the past or may occur in the future and the wetland is awaiting a call to perform this service at
higher levels than presently. An exception would be for a wetland type that would not normally
be considered significant for a particular function (e.g., sediment retention), but due to current
land use of adjacent areas now receives substantial sediment input and thereby performs the
function at a significant level.
W-PAWF also does not consider the condition of the adjacent upland (e.g., level of disturbance)
or the actual water quality of the associated waterbody which may be regarded as important
metrics for assessing the health of individual wetlands (not part of this study). Collection and
analysis of these data were done as another part of this study but were not incorporated into the
preliminary functional assessment.
We further emphasize that the preliminary assessment does not obviate the need for more
detailed assessments of the various functions. This assessment should be viewed as a starting
point for more rigorous assessments, as it attempts to cull out wetlands that may likely provide
significant functions based on generally accepted principles and the source information used for
17
this analysis. This type of assessment is most useful for regional or watershed planning
purposes. For site-specific evaluations, additional work will be required, especially field
verification and collection of site-specific data for potential functions (e.g., following the HGM
assessment approach as described by Brinson 1993a and other onsite evaluation procedures).
This is particularly true for assessments of fish and wildlife habitats and biodiversity. Other
sources of data may exist to help refine some of the findings of this report. Additional modeling
could be done, for example, to identify habitats of likely significance to individual species of
animals (based on their specific life history requirements).
Wetland Restoration Site Inventory
The results of this inventory were derived from air photointerpretation with review of hydric soils
data and updated wetland and land use/cover geospatial data. Time did not permit for field
checking, so results should be considered conservative. Areas identified as potential Type 1
restoration sites had visible evidence of restoration potential (e.g., wet depressions in cropland
and fill sites without buildings).
Type 2 sites could be expanded to include wetlands where the adjacent land use may produce
significant adverse impacts on the quality of the wetland, but this was not an objective of our
project. Many, if not most, wetlands in the watershed could be highlighted as having potentially
significant adverse impacts from adjacent land use practices as many wetlands are surrounded by
cropland. Many of these wetlands, however, were identified as being adversely impacted by
ditching. In addition, by examining the wetland buffer map, one can extract information on land
use practices contiguous with a wetland which could be used to ascertain potentially negative
impacts from external sources.
Rather than piecemeal restoration of small isolated wetlands, wetland restoration of large wetland
blocks (e.g., restoring huge flatwood interfluves) appears more beneficial to a goal of restoring
wetland ecosystems. To accomplish this, hydric soil information should be consulted. These
data will reveal significantly larger areas of hydric soils, presumably former wetlands that are
now cultivated where smaller presently isolated farmed wetlands, small impoundments, and/or
vegetated wetlands could be linked together to form a larger vegetated wetland that can be
connected to an existing wetland. Where hydric soil data are not available in digital form, this
could be done by visual examination of soil survey maps or perhaps by simply drawing lines
around the ditch network to predict the extent of former wetlands. This type of evaluation can be
made by consulting the wetland restoration site map which can be used as a reference for
identification large-scale restoration projects. Field work, however, is required to evaluate the
true restoration potential of any site as there are often limitations and other issues (e.g.,
landowner support) that can only be determined during field inspection.
Ditch Inventory
Photointerpretation of aerial photographs was performed to identify ditches in this watershed.
Although limited field work was performed for this project, such work did not focus on the
18
ditches. Additional work should be done in the future to verify the accuracy and completeness of
this inventory. Based on such work, some revision of the database may be required. In any
event, the existing data present a good perspective on the extent of ditching throughout the
watershed.
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Appropriate Use of this Report
The report provides a basic characterization of wetlands in the Delaware portion of the Nanticoke
watershed including a preliminary assessment of wetland functions. Keeping in mind the
limitations mentioned above, the results are a first-cut or initial screening of the watershed's
wetlands to designate wetlands that may have a significant potential to perform different
functions. The targeted wetlands have been predicted to perform a given function at a significant
level presumably important to the watershed's ability to provide that function. "Significance" is a
relative term and is used in this analysis to identify wetlands that are likely to perform a given
function at a level above that of wetlands not designated. Review of these preliminary findings
and consideration of additional information not available to us may identify the need to modify
some of the criteria used to identify wetlands of potential significance for certain functions.
While the results are useful for gaining an overall perspective of the watershed's wetlands and
their relative importance in performing certain functions, the report does not identify differences
among wetlands of similar type and function. The latter information is often critical for making
decisions about wetland acquisition and designating certain wetlands as more important for
preservation versus others with the same categorization. Additional information may be gained
through consulting with agencies having specific expertise in a subject area and by conducting
field investigations to verify the preliminary assessments. When it comes to actually acquiring
wetlands for preservation, other factors must be considered. Such factors may include: 1) the
condition of the surrounding area, 2) the ownership of the surrounding area and the wetland
itself, 3) site-specific assessment of wetland characteristics and functions, 4) more detailed
comparison with similar wetlands based on field data, and 5) advice from other agencies (federal,
state, and local) with special expertise on priority resources (e.g., for wildlife habitat, contact
appropriate federal and state biologists). The latter agencies may have site-specific information
or field-based assessment methods that can aid in further narrowing the choices to help insure
that the best wetlands are acquired for the desired purpose.
The report is a watershed-based wetland characterization for the Nanticoke watershed. The
report does not make comparisons with other watersheds, although comparisons between
subbasins within this watershed were made from the “natural habitat integrity” standpoint. Be
advised that there may be characteristics (e.g., water quality and habitat concerns) that actually
make acquisition, restoration, or preservation of certain wetlands in one of these subbasins, a
higher priority than protection of similar wetlands in the other subbasins. This was beyond the
scope of the present study.
The report is useful for natural resource planning as an initial screening for considering
prioritization of wetlands (for acquisition, restoration, or strengthened protection), as an
educational tool (e.g., helping better our understanding of wetland functions and the relationships
between wetland characteristics and performance of individual functions), and for characterizing
the differences among wetlands (both form and function). It can also serve as benchmark for
documenting future trends in wetlands, river-stream corridors, and other natural features.
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Rationale for Preliminary Functional Assessments
Nine functions were evaluated: 1) surface water detention, 2) streamflow maintenance, 3)
nutrient transformation, 4) sediment and other particulate retention, 5) shoreline stabilization, 6)
fish and shellfish habitat, 7) waterfowl and waterbird habitat, 8) other wildlife habitat, and 9)
biodiversity. The criteria used for identifying these functions using the digital wetland database
are discussed below. The criteria were developed by the senior author of the report and reviewed
and modified for the subject watersheds based on comments from an ad hoc group of wetland
specialists working on Delaware’s Nanticoke River watershed.
In developing a protocol for designating wetlands of potential significance, wetland size was
generally disregarded from the criteria, with few exceptions (i.e., other wildlife habitat and
biodiversity functions). This approach was followed because it was felt that the State and others
using the digital database and charged with setting priorities should make the decision on
appropriate size criteria as a means of limiting the number of priority wetlands, if necessary. Our
study was intended to present a more expansive characterization of wetlands and their likely
functions and not to develop a rapid assessment method for ranking wetlands for acquisition,
protection, or other purposes. The criteria for identifying different levels of potential
significance can be modified in the future based on review of this report’s findings and field
evaluation. Note that palustrine farmed wetlands have not been identified as being significant for
any function. They were viewed as severely degraded wetlands that perform various functions at
minimal levels. Consequently, they represented sites where substantial gains in wetland
functions may be achieved through restoration projects.
Surface Water Detention
This function is important for reducing downstream flooding and lowering flood heights, both of
which aid in minimizing property damage and personal injury from such events. In a landmark
study on the relationships between wetlands and flooding at the watershed scale, Novitzki (1979)
found that watersheds with 40 percent coverage by lakes and wetlands had significantly reduced
flood flows -- lowered by as much as 80 percent -- compared to similar watersheds with no or
few lakes and wetlands in Wisconsin. Floodplain wetlands, other lotic wetlands (basin and flat
types), estuarine fringe wetlands along coastal rivers, and estuarine island wetlands in these
rivers provide this function at significant levels. Wetlands dominated by trees and/or dense
stands of shrubs (with higher frictional resistance) could be deemed to provide a higher level of
this function as such vegetation may further aid in flood desynchronization versus similar
wetlands with emergent cover. Trees and dense shrubs produce high roughness which helps
dissipate energy and lower velocity of flood waters. Yet, this requirement was not applied to the
data set as emergent wetlands along waterways are also likely to provide significant flood
storage. Floodplain width could also be an important factor in evaluating the significance of
performance of this function by individual wetlands (e.g., for acquisition or strengthened
protection). There is no quantitative information for establishing a significance threshold based
on size, so floodplain width was not used as a selection factor in this study.
For this analysis, the following correlations were used:
21
High - Estuarine Fringe, Estuarine Island, Lotic Floodplain, Lotic Basin, Lotic Fringe,
Lentic Basin wetlands, and Throughflow Ponds (=in-stream)
Moderate - Terrene wetlands that are not ditched (no size criterion; excluding Slope
wetlands) amd Lotic Flat wetlands
Some - Other Ponds and Terrene ditched wetlands (excluding Slope wetlands)
Streamflow Maintenance
Many wetlands are sources of groundwater discharge and some may be in a position to sustain
streamflow in the watershed. Such wetlands are critically important for supporting aquatic life in
streams. Terrene headwater wetlands (by definition, the sources of streams) perform these
functions at notable levels. Lotic wetlands along first order streams may also be important for
streamflow maintenance, so they were also designated as headwater wetlands. Groundwater
discharging into streamside wetlands may contribute substantial quantities of water for sustaining
baseflows. Floodplain wetlands are known to store water in the form of bank storage, later
releasing this water to maintain baseflows. This also aids in reducing flood peaks and improving
water quality (Whiting 1998). Among several key factors affecting bank storage are porosity and
permeability of the bank material, the width of the floodplain, and the hydraulic gradient
(steepness of the water table). The wider the floodplain, the more bank storage given the same
soils. Gravel floodplains drain in days, sandy floodplains in a few weeks to a few years, silty
floodplains in years, and clayey floodplains in decades. In good water years, wide sandy
floodplains may help maintain baseflows.
For this analysis, the following correlations were used:
High - Terrene and Lotic headwater wetlands that are not ditched, Lentic headwater
wetlands, and Outflow Ponds and Lakes (classified as PUB... on NWI), and other
headwater Ponds
Moderate - Lotic Floodplain wetlands, Throughflow Ponds and Lakes (classified as
PUB... on NWI), and Lentic former floodplain wetlands
Some - Terrene and Lotic ditched headwater wetlands
Nutrient Transformation
All wetlands recycle nutrients, but those having a fluctuating water table are best able to recycle
nitrogen and other nutrients. Vegetation slows the flow of water which causes deposition of
mineral and organic particles and nutrients (nitrogen and phosphorus) bound to them, whereas
hydric soils are the places where chemical transformations occur (Carter 1996). Microbial action
in the soil is the driving force behind chemical transformations in wetlands. Microbes need a
22
food source -- organic matter -- to survive, so wetlands with high amounts of organic matter
should have an abundance of microflora to perform the nutrient cycling function. Wetlands are
so effective at filtering and transforming nutrients that artificial wetlands are constructed for
water quality renovation (Hammer 1992). Natural wetlands performing this function help
improve local water quality of streams and other watercourses.
Numerous studies have demonstrated the importance of wetlands in denitrification. Simmons et
al. (1992) found high nitrate removal (greater than 80%) from groundwater during both the
growing season and dormant season in Rhode Island streamside (lotic) wetlands. Groundwater
temperatures throughout the dormant season were between 6.5 and 8.0 degrees C, so microbial
activity was not limited by temperature. Even the nearby upland, especially transitional areas
with somewhat poorly drained soils, experienced an increase in nitrogen removal during the
dormant season. This was attributed to a seasonal rise in the water table that exposed the upper
portion of the groundwater to more organic matter (nearer the ground surface), thereby
supporting microbial activity and denitrification. Riparian forests dominated by wetlands have a
greater proportion of groundwater (with nitrate) moving within the biologically active zone of the
soil that makes nitrate susceptible to uptake by plants and microbes (Nelson et al. 1995).
Riparian forests on well-drained soils are much less effective at removing nitrate. In a Rhode
Island study, Nelson et al. (1995) found that November had the highest nitrate removal rate due
to the highest water tables in the poorly drained soils, while June experienced the lowest removal
rate when the deepest water table levels occurred. Similar results can be expected to occur in the
Nanticoke River watershed. For bottomland hardwood wetlands, DeLaune et al. (1996) reported
decreases in nitrate from 59-82 percent after 40 days of flooding wetland soil cores taken from
the Cache River floodplain in Arkansas. Moreover, they surmised that denitrification in these
soils appeared to be carbon-limited: increased denitrification took place in soils with greater
amounts of organic matter in the surface layer.
Nitrogen fixation is accomplished in wetlands by microbial-driven reduction processes that
convert nitrate to nitrogen gas. Nitrogen removal rates for freshwater wetlands are very high
(averaging from 20-80 grams/square meter) (Bowden 1987). The following information comes
from a review paper on this topic by Buresh et al. (1980). Nitrogen fixation has been attributed
to blue-green algae in the photic zone at the soil-water interface and to heterotrophic bacteria
associated with plant roots. In working with rice, Matsuguchi (1979) believed that the
significance of heterotrophic fixation in the soil layer beyond the roots has been underrated and
presented data showing that such zones were the most important sites for nitrogen fixation in a
Japanese rice field. This conclusion was further supported by Wada et al. (1978). Higher
fixation rates have been found in the rhizosphere of wetland plants than in dryland plants.
Phosphorus removal is largely done by plant uptake (Patrick, undated manuscript). Wetlands
that accumulate peat have a great capacity for phosphorus removal. Wetland drainage can,
therefore, change a wetland from a phosphorus sink to a phosphorus source. This is a significant
cause of water quality degradation in many areas of the world including the United States, where
wetlands are drained for agricultural production. Hydric soils with significant clay constituents
fix phosphorus due to its interaction with clay and inorganic colloids. Reduced soils have more
23
sorption sites than oxidized soils (Patrick and Khalid 1974), while the latter soils have stronger
bonding energy and adsorb phosphorus more tightly.
From the water quality standpoint, wetlands associated with watercourses are probably the most
noteworthy. Numerous studies have found that forested wetlands along rivers and streams
(“riparian forested wetlands”) are important for nutrient retention and sedimentation during
floods (Whigham et al. 1988; Yarbro et al. 1984; Simpson et al. 1983; Peterjohn and Correll
1982). This function by forested riparian wetlands is especially important in agricultural areas.
Brinson (1993b) suggests that riparian wetlands along low order streams may be more important
than those along higher order streams.
Wetlands with seasonally flooded and wetter water regimes (including tidal regimes - seasonally
flooded-tidal, irregularly flooded, and regularly flooded) were identified as having potential to
recycle nutrients at high levels of performance. Estuarine vegetated fringe and island wetlands
were similarly designated for like reasons. The soils of these wetlands should have substantial
amounts of organic matter that would promote microbial activity.
Wetlands with a temporarily flooded water regime including those in tidal environments
(temporarily flooded-tidal) were identified as having a moderate potential for performing this
function. Terrene outflow wetlands surrounded by cropland (50% or more of their upland
perimeter is in contact with cropland) were deemed to have some potential for nutrient
transformation. Since farming often introduces agrochemicals and sediment into streams,
wetlands between cropland and streams lie in landscape positions that favor recycling of
nutrients derived from runoff.
For this analysis, the following correlations were used:
High - All vegetated wetlands and mixed unconsolidated bottom-vegetated wetlands with
seasonally flooded (C), seasonally flooded/saturated (E), semipermanently flooded
(F), seasonally flooded-tidal (R), irregularly flooded (P), and regularly flooded (N)
water regimes (this includes Estuarine, Lotic, Terrene, and Lentic wetlands -
mostly floodplain, basin, interfluve-basin, and fringe types)
Moderate - Lotic flat and floodplain-flat wetlands with temporarily flooded (A) and
temporarily flooded-tidal (S) water regimes
Some - Terrene vegetated wetlands surrounded by >50% farmland
Retention of Sediments and Other Particulates
Many wetlands owe their existence to being located in areas of sediment deposition. This is
especially true for floodplain wetlands. This function supports water quality maintenance by
24
capturing sediments with bonded nutrients or heavy metals (as in and downstream of urban
areas). Estuarine and floodplain wetlands plus lotic and lentic fringe and basin wetlands
(including lotic ponds) are likely to trap and retain sediments and particulates at significant
levels. Lotic flat wetlands are flooded only for brief periods and less frequently than the
wetlands listed above due to their elevation. They were classified as having moderate potential
for sediment retention. For this analysis, lotic flats that were seasonally saturated were also
included in the moderate category, but further evaluation might justify changing their potential to
some since they are not inundated. Terrene outflow wetlands surrounded by cropland may now
perform this function at some level of potential significance due to erosion of tilled soils.
Isolated ponds may be locally significant in retaining such materials, and were also designated as
having possible some potential.
For this analysis, the following correlations were used:
High - Estuarine Fringe, Estuarine Island, Lentic Basin, Lentic Fringe, Lotic Floodplain,
Lotic Basin, Lotic Fringe and Throughflow Pond (in-stream)
Moderate - Lotic Flat, Terrene Basin, Terrene Fringe-pond, and Terrene Interfluve Basin
wetlands, Isolated Ponds, and Outflow Ponds
Some - Terrene Flat and Interfluve Flat wetlands surrounded by >50% cropland
Shoreline Stabilization
Vegetated wetlands along rivers and streams provide this function. Vegetation stabilizes the soil,
thereby preventing erosion. Wetlands adjacent to inland waters serve as buffers to reduce
erosion of uplands from flowing waters and thereby stabilize shorelines. For this analysis, the
following correlations were used:
High - Estuarine vegetated wetlands, Lotic wetlands (vegetated including tidal types;
except island wetlands), Lentic wetlands (vegetated, except island types), and
Terrene Fringe-pond wetlands
Provision of Fish and Shellfish Habitat
The assessment of potential habitat for fish and shellfish was based on generalities that could be
refined for particular species of interest by others at a later date. For tidal areas, the assessment
emphasized palustrine and riverine tidal emergent wetlands, unconsolidated shores (tidal flats)
and estuarine wetlands. For nontidal regions, palustrine aquatic beds5 and semipermanently
flooded wetlands ranked higher than seasonally flooded types due to the longer duration of
surface water. Palustrine forested wetlands along streams (lotic stream wetlands) were deemed
5No palustrine aquatic beds were mapped, but these areas could be important fish habitat.
25
important for maintaining fish and shellfish habitat since their canopies help moderate water
temperatures. Ponds and the shallow marsh-open water zone of impoundments were identified
as wetlands having some potential for fish and shellfish habitat.
Other wetlands providing significant fish habitat may exist, but were not be identified due to the
study methods. Such wetlands may be identified based on actual observations or culled out from
site-specific fisheries information that may be available from the State. Also recall that this
assessment is focused on wetlands, not deepwater habitats, hence the exclusion of the latter from
this analysis, despite widespread recognition that rivers, streams, ponds, and impoundments are
the primary residences of fish and shellfish. Moreover, all wetlands that are significant for the
streamflow maintenance function could be considered vital to sustaining the watershed's ability
to provide in-stream fish and shellfish habitat. While these wetlands may not be providing
significant fish and shellfish habitat themselves, they support base flows essential to keeping
water in streams for aquatic life.
For this analysis, the following correlations were used:
High - Estuarine Emergent, Estuarine Unconsolidated Shore, Palustrine Tidal Emergent
(including mixtures with Scrub-Shrub and Forested), Riverine Tidal
Unconsolidated Shore, Riverine Tidal Emergent, Palustrine Semipermanently
Flooded, Palustrine Aquatic Bed, Palustrine Unconsolidated Bottom/vegetated
wetland (Emergent, Scrub-Shrub, or Forested), Palustrine vegetated wetland with
a Permanently Flooded water regime, and Ponds associated with Semipermanently
Flooded vegetated wetlands
Moderate - Lotic Stream wetlands that are Palustrine Emergent (including mixtures with
Scrub-Shrub or Forested wetlands that are seasonally flooded/saturated), and
Throughflow Ponds
Some - Outflow Ponds and Isolated Ponds
Important for Stream Shading - Lotic Stream wetlands that are Palustrine Forested
wetlands (includes mixes where forested wetland predominates; excluding those
along intermittent streams)
Provision of Waterfowl and Waterbird Habitat
Wetlands considered to be important waterfowl and waterbird habitat were estuarine wetlands
(vegetated or not), riverine emergent wetlands, estuarine and riverine unconsolidated shores6
6The only estuarine or riverine unconsolidated shore mapped was a temporarily flooded-tidal
26
(excluding temporary flooded-tidal), palustrine tidal and riverine tidal emergent wetlands
(including emergent/shrub mixtures), semipermanently flooded wetlands, mixed open water-emergent
wetlands (palustrine and lacustrine), and aquatic beds. For this analysis, palustrine
tidal scrub-shrub/emergent wetlands and tidal forested/emergent wetlands were designated as
having moderate significance for these birds, yet they should be evaluated to determine if their
status should be upgraded to high potential. Ponds were considered to have some potential for
providing waterfowl and waterbird habitat.7
Wetlands that may be significant to wood duck were identified, since wooded streams are
particularly important for them. Seasonally flooded lotic wetlands that were forested or mixtures
of trees and shrubs (excluding those along intermittent streams) were deemed as wetlands with
significant potential for use by wood ducks. Wetlands listed as having high potential for
waterfowl and waterbird habitat also include some types important to wood ducks (e.g.,
semipermanently flooded lotic shrub/emergent wetlands).
Seasonally flooded emergent wetlands (including mixtures with shrubs) were not designated as
potentially significant for waterfowl and waterbirds. Field checking of these types may reveal
that some are freshwater marshes that may provide significant habitat. If so, these types may be
added to the wetlands of significance in the future. Other wetlands worthy of further
consideration are forested wetlands bordering estuarine wetlands. They may be important for
colonial nesting birds. If they provide such habitat in the Nanticoke watershed, then they should
be added to the list.
For this analysis, the following correlations were used:
High - Estuarine Emergent, Estuarine Unconsolidated Shore, Riverine Tidal Emergent,
Riverine Tidal Unconsolidated Shore (Regularly Flooded), Palustrine
Semipermanently Flooded, Palustrine Aquatic Bed, Palustrine Tidal Emergent,
Palustrine Tidal Emergent/Scrub-Shrub, Palustrine vegetated wetlands that are
Permanently Flooded, and Ponds associated with Semipermanently Flooded
riverine one.
7Ponds on wildlife management areas (e.g., refuges) should be considered to be of moderate
significance due to their management. Since we did not have the location of such refuges in our
digital database, these ponds could not be separated from the rest of the ponds. Hence, all ponds
were designated as having some potential for this function.
27
vegetated wetlands
Moderate - Palustrine Tidal Scrub-Shrub/Emergent and Forested/Emergent
Some - Other Palustrine Unconsolidated Bottom
Significant for Wood Ducks - Lotic wetlands (excluding those along intermittent streams)
that are Forested or Scrub-shrub wetlands or mixtures of these two types
(including freshwater tidal and nontidal), and Lotic wetlands that are
Forested/Emergent with a Seasonally Flooded/Saturated or wetter water regime
(including Seasonally Flooded-Tidal) and Unconsolidated Bottom/Forested
Provision of Other Wildlife Habitat
The provision of other wildlife habitat by wetlands was evaluated in general terms. Species-specific
habitat requirements were not considered. In developing an evaluation method for
wildlife habitat in the glaciated Northeast, Golet (1972) designated several types as outstanding
wildlife wetlands including: 1) wetlands with rare, restricted, endemic, or relict flora and/or
fauna, 2) wetlands with unusually high visual quality and infrequent occurrence, 3) wetlands with
flora and fauna at the limits of their range, 4) wetlands with several seral stages of hydrarch
succession, and 5) wetlands used by great numbers of migratory waterfowl, shorebirds, marsh
birds, and wading birds. Golet subscribed to the principle that in general, as wetland size
increases so does wildlife value, so wetland size was important factor for determining wildlife
habitat potential in his approach. Other important variables included dominant wetland class,
site type (bottomland v. upland; associated with waterbody v. isolated), surrounding habitat type
(e.g., natural vegetation v. developed land), degree of interspersion (water v. vegetation), wetland
juxtaposition (proximity to other wetlands), and water chemistry.
For this project, wetlands important to waterfowl and waterbirds were identified in a separate
assessment (see above). Emphasis for assessing "other wildlife" was placed on conditions that
would likely provide significant habitat for other vertebrate wildlife (mainly herps, interior forest
birds, and mammals). Opportunistic species that are highly adaptable to fragmented landscapes
were not among the target organisms, since there seems to be more than ample habitat for these
species now and in the future. Rather, animals whose populations may decline as wetland
habitats become fragmented by development are of more concern. For example, breeding
success of neotropical migrant birds in fragmented forests of Illinois was extremely low due to
high predation rates and brood parasitism by brown-headed cowbirds (Robinson 1990).
Newmark (1991) reported local extinctions of forest interior birds in Tanzania due to
fragmentation of tropical forests. Fragmentation of wetlands is an important issue for wildlife
managers to address. Some useful references on fragmentation relative to forest birds are Askins
et al. (1987), Robbins et al. (1989), Freemark and Merriam (1986), and Freemark and Collins
(1992). The latter study includes a list of area-sensitive or forest interior birds for the eastern
United States. The work of Robbins et al. (1989) is particularly relevant to the study watersheds
as they addressed area requirements of forest birds in the Mid-Atlantic states. They found that
28
species such as the black-throated blue warbler, cerulean warbler, Canada warbler, and black-and-
white warbler required very large tracts of forest for breeding. Table 2 lists some area-sensitive
birds for the region. Ground-nesters, such as veery, black-and-white warbler, worm-eating
warbler, ovenbird, waterthrushes, and Kentucky warbler, are particularly sensitive to
predation which may be increased in fragmented landscapes. Robbins et al. (1989) suggest a
minimum size of 7,410 acres to retain all species of the forest-breeding avifauna in the Mid-
Atlantic region.
The analysis identified two wetland types as potentially highly significant for other wildlife: 1)
large wetlands (> 20 acres) regardless of vegetative cover but excluding pine plantations, and 2)
smaller diverse wetlands (10-20 acres with multiple cover types). These two categories covered
most wetlands along stream corridors that connect large wetland complexes. Other vegetated
wetlands were designated as having some potential significance for providing wildlife habitat.
Given the general nature of this assessment of "other wildlife habitat," the State may want to
refine this assessment in the future by having biologists designate "target species" that may be
used to identify important wildlife habitats in the Nanticoke watershed. After doing this, they
could identify criteria that may be used to identify potentially significant habitat for these species
in the watershed. Dr. Hank Short (U.S. Fish and Wildlife Service, retired) compiled a matrix
listing 332 species of wildlife and their likely occurrence in wetlands of various types in New
England from ECOSEARCH models (Short et al. 1996) that he developed with Dr. Dick
DeGraaf (U.S. Forest Service) and Dr. Jay Hestbeck (U.S. Fish and Wildlife Service).8 DeGraaf
and Rudis (1986) summarized habitat, natural history, and distribution of New England wildlife.
Much of what is in the ECOSEARCH models comes from this source. These sources may be
useful starting points for determining relationships between wildlife and wetlands and may be
expanded to cover the Mid-Atlantic region.
For this analysis, the following correlations were used:
High - Large wetlands (>20 acres, excluding pine plantations) and small diverse wetlands
(10-20 acres with 2 or more covertypes),
Some - Other vegetated wetlands
8Copies of the matrix can be obtained by contacting R. Tiner (address on title page).
29
Table 2. List of some area-sensitive birds for forests of the Mid-Atlantic region. (Source:
Robbins et al. 1989).
Area (acres) at which
probability of occurrence
Species is reduced by 50%
Neotropical Migrants
Acadian flycatcher 37
Blue-gray gnatcatcher 37
Veery 49
Northern parula 1,280
Black-throated blue warbler 2,500
Cerulean warbler 1,700
Black-and-white warbler 543
Worm-eating warbler 370
Ovenbird 15
Northern waterthrush 494
Louisiana waterthrush 865
Canada warbler 988
Summer tanager 99
Scarlet tanager 30
Short-distance Migrants
Red-shouldered hawk 556
Permanent Residents
Hairy woodpecker 17
Pileated woodpecker 408
30
Conservation of Biodiversity
In the context of this report, the term "biodiversity" is used to identify certain wetland types that
appear to be scarce or relatively uncommon in the watershed, or individual wetlands that possess
several different covertypes (i.e., diverse wetland complexes), or complexes of large wetlands.
Schroeder (1996) noted that to conserve regional biodiversity, maintenance of large-area habitats
for forest interior birds is essential. As noted above, Robbins et al. (1989) suggest a minimum
forest size of 7,410 acres to retain all species of the forest-breeding avifauna in the Mid-Atlantic
region.
For recognizing the conservation of biodiversity function, we attempted to highlight areas that
may contribute to the preservation of an assemblage of wetlands that encompass the natural
diversity of wetlands in the Nanticoke watershed. Forested areas 7,410 acres and larger that
contained contiguous palustrine forested wetlands and upland forests were designated as
important for maintaining regional biodiversity of avifauna based on recommendations by
Robbins et al. (1989). We also identified a few other large wetlands in the watershed (e.g.,
possibly important for interior nesting birds and wide-ranging wildlife in general) and wetlands
that were uncommon types (based on mapping classification and not on Natural Heritage
Program data). All riverine tidal wetlands and oligohaline wetlands were identified as
significant for this function because they are often colonized by a diverse assemblage of plants
and are among the most diverse plant communities in the Mid-Atlantic region.
Use of Natural Heritage Program data and GAP data have been suggested, but these data were
not provided for the Nanticoke watershed in digital form for our use. Consequently, there was no
attempt to incorporate such data into our analysis. It is expected that Natural Heritage and GAP
information will be utilized at a later date by the State for more detailed planning and evaluation.
Consequently, the wetlands designated as potentially significant for biodiversity are simply a
foundation to build upon. Local knowledge of significant wetlands will further refine the list of
wetlands important for this function. For information on rare and endangered species, contact
the Delaware Natural Heritage Program.
For this analysis, the following correlations were used:
Wetlands with Atlantic white cedar or bald cypress, Estuarine oligohaline emergent
wetlands, Riverine tidal emergent wetlands, Palustrine tidal emergent wetlands (including
emergent and scrub-shrub mixtures), Palustrine emergent wetlands seasonally flooded
and wetter that are not ditched, diked, or excavated (including mixtures with scrub-shrub),
Palustrine tidal scrub-shrub wetlands, Semipermanently flooded Palustrine scrub-shrub
wetlands, Semipermanently flooded Palustrine forested wetlands (including
mixtures), Seasonally flooded and wetter Palustrine forested/emergent wetlands,
Palustrine tidal deciduous/evergreen forested wetlands, Palustrine tidal mixed
forested/scrub-shrub wetlands, Palustrine tidal evergreen forested wetlands, and
Palustrine wetlands within any 7,410-acre tract of contiguous forestland (both wetland
and upland forests)
31
Results
Wetland Classification and Inventory
Wetlands were classified according to the U.S. Fish and Wildlife Service's official wetland
classification system (Cowardin et al. 1979) and by landscape position, landform, and water flow
path descriptors following Tiner (2000). Summaries for the study area are given in Tables 3 and
4 and illustrated in Maps #1 through #4. The maps are presented on a compact disk which also
contains a copy of this report. Table 3 summarizes covertypes through the subclass level of the
Service’s classification ("NWI types"), while Table 4 tabulates statistical data on wetlands by
landscape position and landform ("HGM types"). Twenty-four percent of the watershed area
(which includes the river itself) is occupied by wetlands. If the river and its tributaries are
excluded from the watershed area, the percent of “land” represented by wetlands amounts to 25
percent.
Wetlands by NWI Types
According to the NWI, the Nanticoke watershed had 77,359 acres of wetlands, excluding linear
features (Table 3; Map #1). Nearly all of the wetlands were palustrine types, with only 80 acres
of estuarine wetlands and 34 acres of riverine wetlands. Seventy-nine percent of the wetlands
was forested (including mixed forested/scrub-shrub types). Many of the existing palustrine
scrub-shrub and scrub-shrub/emergent wetlands represent successional plant communities of cut-over
forested wetlands in various stages of regrowth. Ninety-eight percent of the wetlands was
nontidal (beyond tidal influence), while only two percent was tidal. About 71 percent of the
watershed’s wetlands was impacted by ditching, farming, impoundment, or excavation, with 65
percent alone being partly drained due to ditching and channelization. Four percent of the
wetlands was farmed. Only 419 wetland acres were impounded, while 666 acres were excavated.
Most (82%) of the watershed’s wetlands were seasonally saturated with high water tables in
winter and early spring (Table 4). Ten percent was seasonally flooded types. Only 2 percent of
the Nanticoke watershed’s wetlands was tidal. (Note: Palustrine farmed wetlands were not
included in the above statistics, since no water regime was attributed to them.)
The watershed also had 2,382 acres of deepwater habitats: 1,222 acres of tidal rivers, 138 acres
of nontidal rivers, 328 acres of estuarine river, and 693 acres of impounded lakes. In addition,
the watershed contained 532 miles of linear nontidal streams.
32
Table 3. Wetlands in the Nanticoke watershed classified by NWI wetland type to the class level
(Cowardin et al. 1979). Other modifiers have been deleted from NWI types for this compilation.
NWI Wetland Type Acreage
Estuarine Wetlands
Emergent (Oligohaline) 79.9
----------------------------- --------
Subtotal 79.9
Palustrine Wetlands
Emergent (Nontidal) 1,040.0
Emergent (Tidal) 87.5
Farmed 3,309.6
Scrub-Shrub/Emergent 4,210.9 (including 59.8 tidal)
Broad-leaved Deciduous Forested (Nontidal) 25,154.1 (including 267.7 cypress)
Broad-leaved Deciduous Forested (Tidal) 1,083.2
Needle-leaved Evergreen Forested 4,673.9 (including 12.6 tidal)
Mixed Forested (Nontidal) 17,622.6
Mixed Forested (Tidal) 182.5
Deciduous Forested/Emergent 320.0 (including 0.9 tidal)
Forested/Scrub-Shrub and Forested/Scrub-Shrub 12,343.1 (including 11.7 tidal;
25.5 cypress)
Deciduous Scrub-Shrub 1,496.5 (including 41.0 tidal)
Needle-leaved Evergreen Scrub-Shrub (Nontidal) 3,010.1
Scrub-Shrub (Nontidal) 2,047.9
Unconsolidated Bottom/Vegetated 40.4 (including 34.8 cypress)
Unconsolidated Bottom (Nontidal) 622.9 (including 7.9 uncon. shore)
----------------------------------------------------------- ------------------------------------------
Subtotal 77,245.2
Riverine Wetlands
Emergent (Tidal) 33.5
Unconsolidated Shore (Tidal) 0.3
-------------------------------------- -------------
Subtotal 33.8
GRAND TOTAL (ALL WETLANDS) 77,358.9
33
Table 4. Distribution of Nanticoke wetlands according to water regime.
Water Regime Percent of
Watershed’s Wetlands*
Temporarily Flooded 3.7
Saturated (Seasonally) 82.4
Seasonally Flooded 5.5
Seasonally Flooded/Saturated 4.9
Semipermanently Flooded 0.5
Permanently Flooded 0.7
Artificially Flooded 0.1
Regularly Flooded (tidal) 0.1
Irregularly Flooded (tidal) 0.1
Seasonally Flooded-Tidal 1.9
Temporarily Flooded-Tidal 0.1
*Excludes palustrine farmed wetlands.
34
Hydrogeomorphic-Type Wetlands9
A total of 3,947 wetlands (excluding ponds) was inventoried in the Nanticoke River watershed
and classified by their hydrogeomorphic features (Table 5; Maps #2-#4). Nearly 83 percent of
the individual wetlands (excluding ponds) occurred in terrene landscape positions (Map #2).
These wetlands accounted for 85 percent of the watershed’s wetland acreage. Lotic wetlands
were second-ranked in extent, making up 14 percent of the acreage and 16 percent of the number.
The remaining 1 percent of the acreage was comprised of estuarine wetlands (0.7% of the
acreage) lying along estuarine waters and lentic wetlands (0.3% of the acreage) associated lake
basins including large impoundments.
From the landform standpoint, interfluve wetlands accounted for 74 percent of the wetland
acreage (excluding ponds) (Map #3). Floodplain wetlands were next in abundance representing
13 percent of the acreage, while flats and basins comprised 7 percent and 5 percent, respectively.
Outflow wetlands were the predominant water flow path type (Map #4). They totaled nearly
62,000 acres and represented 81 percent of the wetland acreage. Throughflow wetlands ranked
next at 14 percent (10,532 acres), followed by isolated wetlands (3%; 2,678 acres) and
bidirectional flow wetlands (2%; 1,597 acres). Ponds were nearly equally divided between
outflow types (43%) and isolated types (39%), with the rest being throughflow types (18%).
Wetlands fragmented by major roads amounted to 4,411 acres. This represents about 6 percent
of the wetland acreage. If fragmentation was considered from the landscape perspective, the
figure would be much higher as many remnants of once larger wetland complexes (i.e.,
interfluves) are now surrounded by cropland. Also many minor roads cris-cross wetlands
throughout the watershed.
9All wetlands, except palustrine unconsolidated bottoms and shores, were characterized
by HGM-type descriptors. These exceptions were classified as pond or lake types and are
not reflected in the summary statistics.
35
Table 5. Wetlands (excluding ponds) in the Nanticoke watershed classified by landscape
position, landform, and water flow path (Tiner 2000). See Appendix for definitions.
Landscape Landform Water Flow # of Wetlands Acreage
Position
Estuarine 11 513.7
Fringe* Bidirectional 11 513.7
Lentic 50 252.3
Basin Bidirectional 3 5.8
Throughflow 21 94.3
Flat Throughflow 9 23.7
Fringe Throughflow 14 123.5
Island Throughflow 3 5.0
Lotic River 174 944.8
Floodplain Bidirectional** 117 812.3
Throughflow 6 28.0
Fringe Bidirectional** 50 104.2
Island Bidirectional** 1 0.3
Lotic Stream 443 9,708.6
Perennial 400 9,532.1
Basin Throughflow 25 66.5
Flat Throughflow 55 562.6
Floodplain Throughflow 298 8,745.5
Fringe Throughflow 22 157.5
Intermittent 4 15.6
Basin Throughflow 2 11.8
Flat Throughflow 2 3.8
36
Tidal 39 160.9
Floodplain Bidirectional 26 139.8
Fringe Bidirectional 13 21.1
Terrene 3269 65,328.3
Basin Isolated 820 956.5
Outflow 682 2,629.9
Throughflow 36 61.3
Flat Isolated 294 996.7
Outflow 289 3,321.4
Throughflow 53 303.7
Fringe Outflow 1 0.9
Interfluve Isolated 56 724.6
Outflow 1010 55,988.7
Throughflow 28 344.6
*Includes tidal freshwater wetlands contiguous with estuarine wetlands and along estuarine waters
**Freshwater tidal reach
37
Maps
Twenty-two maps were produced at 1:90,000 to profile the Nanticoke’s wetlands and watershed.
These maps have been distributed to the Delaware Department of Natural Resources and
Environmental Control. They are also included in a separate folder on the CD containing this
report. The report and accompanying maps may be put up on the NWI homepage
(wetlands.fws.gov) under “reports and publications” in the near future.
A list of the 22 maps follows:
Map 1 - Wetlands and Deepwater Habitats Classified by NWI Types
Map 2 - Wetlands Classified by Landscape Position
Map 3 - Wetlands Classified by Landform
Map 4 - Wetlands Classified by Water Flow Path
Map 5 - Potential Wetlands of Significance for Surface Water Detention
Map 6 - Potential Wetlands of Significance for Streamflow Maintenance
Map 7 - Potential Wetlands of Significance for Nutrient Transformation
Map 8 - Potential Wetlands of Significance for Sediment and Other Particulate Retention
Map 9 - Potential Wetlands of Significance for Shoreline Stabilization
Map 10 - Potential Wetlands of Significance for Fish and Shellfish Habitat
Map 11 - Potential Wetlands of Significance for Waterfowl and Waterbird Habitat
Map 12 - Potential Wetlands of Significance for Other Wildlife Habitat
Map 13 - Potential Wetlands of Significance for Biodiversity
Map 14 - Potential Wetland Restoration Sites
Map 15 - Extent of Ditching
Map 16 - Condition of Perennial River and Stream Corridors (200m)
Map 17 - Condition of Wetland Buffers (100m)
Map 18 - Condition of Pond and Lake Buffers (100m)
Map 19 - Extent of Natural Vegetation in the Watershed
Map 20 - Condition of Streams (Channelized or Dammed vs. Natural)
Map 21 - Condition of Vegetated Wetlands (Partly Drained/Excavated/Impounded vs. Not
Altered)
Map 22 - Potential Sites for Restoring Wildlife Travel Corridors
The first four maps depict wetlands by the Service’s classification system (NWI types) and by
landscape position, landform, and water flow path. Maps 5-13 highlight wetlands that may
perform each of the referenced functions at a significant level. Maps 14-22 address some other
important natural resource features of the watershed.
Summary of Preliminary Functional Assessment Data
38
The rationale for preliminary assessment of wetlands for performing each of nine functions and
designated wetland types of potential significance are given in the Methods section. Table 6
summarizes the results for each function for the watershed (see Maps 5-13), while the findings
for each subbasin are given in Appendix B.
Nearly 96 percent of the wetland acreage was identified as potentially significant for surface
water detention, while almost 91 percent was deemed as potentially significant for streamflow
maintenance. The headwater position of this portion of the Nanticoke watershed led to most
wetlands being designated as important for the latter function. For nutrient transformation, about
65 percent of the wetland acreage may have at least some potential, and a nearly equal amount
(67%) was identified as potentially significant for sediment and other particulate retention.
Approximately 15 percent of the wetland acreage may have potential for shoreline stabilization.
About 14 percent of the wetlands was predicted to have at least some potential as habitat for or
provide significant benefits to fish and shellfish. Please note that wetlands designated as
significant for the streamflow maintenance should also be considered vital to sustaining the
watershed's ability to provide in-stream fish habitat. Fifteen percent of the wetland acreage may
have some potential for providing waterfowl and waterbird habitat, with most of the designated
wetlands potentially benefitting wood duck. Almost 84 percent of the wetlands were identified
as potentially important as habitat for other wildlife. Wetlands listed as potentially important for
biodiversity represented about 39 percent of the wetland acreage. For this function, one large
contiguous forest of 21,069 acres contained 12,777 acres of wetland (85% of which was forested
or mixed forested/scrub-shrub types), while six large wetland complexes of the following sizes
were identified: 1,342 acres, 1,554 acres, 1,545 acres, 986 acres, 1,428 acres, and 4,458 acres.
These complexes plus the wetlands in the large contiguous forest accounted for 31 percent of the
watershed’s wetlands, while rare or uncommon wetland types comprised only 8 percent.
Readers should keep in mind that this assessment was based on remote sensing techniques and
specific studies that may have been published on various functions were not reviewed. In
particular, known sites important to maintaining biodiversity such as those on record with the
Delaware Natural Heritage Program were not consulted. Consequently, the listing is
conservative and represents a starting point, not an end point for an assessment of wetlands
important for various functions. These sources could be reviewed by the State at a later date to
add or delete wetlands from the list in their future planning and evaluation efforts.
39
Table 6. Preliminary functional assessment results for wetlands of the Nanticoke watershed.
% of Wetland
Function Potential Significance Acreage Acreage
Surface Water Detention High Potential 10,803 14.0
Moderate Potential 15,770 20.4
Some Potential 47,328 61.2
Streamflow Maintenance High Potential 15,772 20.4
Moderate Potential 7,520 9.7
Some Potential 46,915 60.6
Nutrient Transformation High Potential 9,625 12.4
Moderate Potential 2,020 2.6
Some Potential 38,832 50.2
Retention of Sediments
and Inorganic Particulates High Potential 10,931 14.1
Moderate Potential 2,681 3.5
Some Potential 38,358 49.6
Shoreline Stabilization High Potential 11,364 14.7
Fish/Shellfish Habitat High Potential 666 0.9
Moderate Potential 57 0.1
Some Potential 513 0.7
Shading Potential* 9,239 11.9
Waterfowl/Waterbird Habitat High Potential 644 0.8
Moderate Potential 55 0.1
Some Potential 596 0.8
Wood Duck Potential 10,279 13.3
Other Wildlife Habitat High Potential 60,670 78.4
Some Potential 3,945 5.1
Biodiversity Wetlands with Atlantic White Cedar 120 0.2
Wetlands with Bald Cypress 328 0.4
Estuarine Oligohaline Wetlands 80 1.0
Riverine Tidal Wetlands 34 -
Uncommon Fresh Tidal Wetlands 212 2.7
Uncommon Nontidal Wetlands 264 3.4
Wetter Palustrine Emergent Wetlands 95 0.1
Wetlands within 7,410+ acre Forest 12,777 16.5
Large Wetland Complexes (six: 1327 a;
1554; 1545; 986; 1428; 4458 a) 11,297 14.6
Potential Wetland Restoration Sites
40
Due to the history of human activities in this watershed, there are many opportunities for wetland
restoration. Over 55,000 acres of potential wetland restoration sites were identified (Map 14). A
total of 4,178 acres of Type 1 wetland restoration sites were identified in the Nanticoke
watershed and 50,909 acres of Type 2 sites (Table 7). Two-thirds of the watershed’s wetlands
were designated as Type 2 sites (degraded wetlands whose functions may be improved by various
types of restoration). Farmed wetlands (constituting 4 percent of the watershed’s wetlands) were
identified as potential Type 1 restoration sites, since their current wetland functions are minimal
due to severe modification. They represented 79 percent of the Type 1 restoration acreage.
The extent of ditching in this watershed is significant (see following subsection). As a result,
almost 99 percent of the Type 2 potential restoration sites consisted of partly drained (ditched)
wetlands. The effect of drainage on these wetlands must be evaluated in the field on a case-by-case
basis. Some of these wetlands may have minimal adverse effects, while many others may be
seriously impacted by the drainage ditches. For example, ditched wetlands with a seasonally
flooded/saturated water regime (e.g., PFO1Ed) may be less adversely impacted than those
classified with a temporarily flooded water regime (e.g., PFO1Ad). The extent of ditching has
been highlighted for potential restoration sites on the wetland restoration site map (Map 14) to
provide some visual perspective on the magnitude of ditching in the affected wetlands.
Some of the impounded wetlands listed under Type 2 sites may include both former vegetated
wetlands and uplands, whereas some of the impoundments designated as potential Type 1
restoration sites include former stream or river channels. Field investigations or an examination
of historical aerial photographs are required to sort out the differences. Nonetheless, most of the
latter types occupied landscape positions (i.e., adjacent to floodplains) where they could be
restored to provide floodplain wetland functions, if desirable.
Narrow man-made levees along channelized streams also represent potential Type 1 wetland
restoration sites, but were not included in the above statistics. Construction of many of these
levees involved depositing spoil material produced from stream channelization projects onto
wetlands. Complete removal of this fill would produce some gains in wetland acreage and
restore wetland hydrology to some degree. At a minimum, the hydrology of the affected
wetlands could be improved by creating openings in the levees in a sufficient number of places to
reconnect these landward wetlands with their adjacent streams. Clearly, this would improve the
surface water detention function of these wetlands.
41
Table 7. Acreage and number of potential wetland restoration sites in the Nanticoke watershed.
Potential Type 1 Restorations No. of Sites* Acreage
Effectively drained or filled former wetlands
(now dryland)** 57 84.5
Farmed wetlands 1,397 3,309.6
Impoundments (former vegetated
wetlands)*** 10 653.3
Excavated former vegetated wetlands 7 130.5
-------------------------------------------- ----------- -------------------
Total 1,471 4,177.9
Potential Type 2 Restorations No. of Sites* Acreage
Impounded Wetlands and Ponds
(formerly vegetated wetlands) 98 418.7
Ditched Palustrine Wetlands 2,886 50,155.7
Excavated Wetlands 371 334.2
------------------------------------- ----------- ------------
Total 3,355 50,908.6
*Sites relate to mapped polygons; one large wetland complex therefore may contain a
number of sites.
**Does not include narrow man-made levees along channelized streams.
***Includes undetermined acreage of former riverbed or streambed.
42
Extent of Ditching
A total of 1,128 miles of ditches was inventoried by this project. This figure amounts to 2.3
miles of ditches per square mile of land area. Map 15 shows the extent of ditching in the
Nanticoke watershed. Also note that besides the ditches, the watershed had 438 miles of
channelized nontidal rivers and streams, representing 80 percent of the total nontidal perennial
river and stream length in the watershed. The channelized stream segments can be interpreted as
opportunities for stream restoration. Priorities for such restoration might start with channelized
perennial and seasonally flooded/saturated intermittent streams.
Water Resource Buffer Analysis
Buffers were established around several water resource features to evaluate the condition of lands
immediately surrounding wetlands and waterbodies. The buffer excludes open water areas. .
Maps 16 through 18 show the condition of the 100m buffer around the following features: 1)
perennial rivers and streams (nontidal), 2) vegetated wetlands, and 3) ponds and lakes,
respectively. While the 100m buffer often includes some open water, our analysis focused on the
“land” portion of the buffer since this is the zone that may be vegetated or developed.
Approximately 59 percent of 100m buffer around perennial rivers and streams10 still possessed
natural vegetation intact, while 80 percent of the “developed” buffer consisted agricultural land.
Only 36 percent of the 100m buffer around vegetated wetland remains vegetated, while slightly
more (39%) of the buffer around ponds and lakes is vegetated.
Analyses were performed for buffers around various combinations of waterbodies, with the
following results: 1) perennial nontidal and tidal rivers and streams: 59 percent vegetated, 2)
perennial and intermittent nontidal rivers and streams and ditches: 41 percent vegetated, 3)
perennial and intermittent rivers and streams, tidal rivers, and ditches: 42 percent vegetated, and
4) perennial streams only (including intermittents with prolonged flows: R4SBEx, and excluding
impounded stream segments): 59 percent.
Readers should note that buffer areas mapped as agricultural land may represent opportunities to
restore natural vegetation along streams, wetlands, and other waterbodies. Such areas should
10Perennial streams include streams designated as seasonally flooded/saturated intermittent
streams (i.e., R4SBEx) which flow for long periods during the year, but not year-round. Such
streams were identified on the source data (U.S.Geological Survey DLGs) as perennial, but based
on our field experiences and those of Amy Jacobs (DNREC), they were determined to be
intermittent.
43
typically be cropland that may be readily revegetated with native woody species to restore
effectiveness of natural buffers.
Natural Habitat Integrity Indices
These indices were calculated for the entire Delaware portion of the watershed and for each
corresponding subbasin. Note stream corridor and various buffer analyses focus on the “land”
portion of the buffer (i.e., the area that may contain self-supporting vegetation) and excludes any
open water areas in that zone.
Values for the Entire Watershed
The values for the nine indices for the Delaware portion of the Nanticoke River watershed are
calculated and presented below.
Natural Cover Index = 128,028 acres of natural vegetation/312,779 acres of land in
watershed = 0.41
River-Stream Corridor Integrity Index for Perennials Only (100m buffer = 200m corridor)
= 28,092 acres of natural vegetation in buffer/47,302 acres of buffer = 0.59
Vegetated Wetland Buffer Index (100m) = 28,779 acres of natural vegetation in upland
buffer/79,380 acres of upland buffer = 0.36
Pond and Lake Buffer Index (100m) = 2,460 acres of natural vegetation in upland
buffer/6,289 acres of upland buffer = 0.39
Wetland Extent Index = 59,529 acres of wetlands/143,945 acres of hydric soil map units
= 0.41 (Note: Estimated from hydric soil data available for 85 percent of the watershed)
Standing Waterbody Extent Index = 1.0 due to impoundment and pond construction
Dammed Stream Flowage Index = 17.6 miles dammed/574.3 miles of perennial nontidal
rivers and streams = 0.03
Channelized Stream Length Index = 437.8 miles of channelized streams/556.7 miles of
perennial nontidal rivers and streams = 0.79
Wetland Disturbance Index = 54,550 acres of altered wetlands/77,362 acres of wetlands =
0.71
44
Composite Natural Habitat Integrity Index = ICNHI 100 = (0.5 x INC) + (0.125 x IRSCI200) +
(0.125 x IWB100) + (0.05 x IPLB100)+ (0.1 x IWE), + (0.1 x ISWE) - (0.1 x IDSF) - (0.1 x ICSL) - (0.1 x
IWD) = (0.5 x 0.41) + (0.125 x 0.59) + (0.125 x 0.36) + (0.05 x 0.39) + (0.1 x 0.41) + (0.1
x 1.0) - (0.1 x 0.03) - (0.1 x 0.79) - (0.1 x 0.71) = 0.485 - 0.153 = 0.33
The above indices provide evidence of a severely stressed system. A pristine watershed has an
index value of 1.0 for natural habitat integrity. The value of 0.33 for the Nanticoke watershed
indicates significant human modification. While stream corridors seem to be in somewhat
reasonable shape regarding natural vegetation (59% of the 200m corridor is in natural
vegetation), nearly two-thirds of the vegetated wetland buffer and 61 percent of the pond and
lake buffers have been developed. Overall, the Nanticoke watershed has lost 59 percent of both
its natural habitat and its original wetlands, while 79 percent of its streams have been
channelized, and 71 percent of its current wetlands are altered by ditches, diking, excavation, or
farming. Forty-one percent of the land in the watershed is covered with “natural vegetation,” 50
percent is in agriculture, and 9 percent is developed. If the response of this watershed to farming
and development is similar to that of Wisconsin watersheds studied by Wang et al. (1997), we
can expect significant degradation of water quality, since they found that watersheds with more
than half of their acreage in agriculture experienced significant declines in instream habitat
quality versus watersheds with less agriculture and more forest.
Summaries for Each Subbasin
A summary of vital statistics for each subbasin are presented in Tables 8 through 15, with results
of the preliminary assessment of wetland functions for each subbasin presented in Appendix B.
Wetland characteristics are outlined in Table 8. Land use and land cover features are presented
in Table 9. The condition of various stream buffers is presented in Table 10, while the condition
of the 100m buffer around lakes and ponds, and around wetlands are given in Tables 11 and 12,
respectively. Alterations of streams and the extent of ditching is tabulated in Table 13. Wetland
alterations are outlined in Table 14. Remotely-sensed natural habitat integrity indices are
summarized in Table 15. Application of the natural habitat integrity indices to individual
subbasins within the watershed could aid in targeting areas for preservation and restoration.
From the indices for the entire watershed, we have seen that this watershed is extremely impacted
by human activities, mainly agriculture. Gravelly Branch, with composite index value of 0.51,
appears to be in noticeably better condition than the other subbasins. All other subbasins have
composite index scores less than 0.40. Marshyhope Creek and Nanticoke River subbasins appear
to be in the worst condition, with composite index values of less than 0.30.
45
Table 8. Wetland acreage for each subbasin of the Nanticoke watershed by NWI type. Coding:
E2EM = Estuarine Emergent; PEM/SS-M = Palustrine Mixed Emergent and Scrub-Shrub; PEM =
Palustrine Emergent; Pf = Palustrine Farmed; PFO-M = Palustrine Mixed Forested; PFO/EM-M =
Palustrine Mixed Forested/Emergent; PFO/SS-M = Palustrine Mixed Forested/Scrub-Shrub; PFO-D =
Palustrine Deciduous Forested; PFO-E = Palustrine Evergreen Forested; PSS-M = Palustrine Mixed Scrub-
Shrub; PSS-D = Palustrine Deciduous Scrub-Shrub; PSS-E = Palustrine Evergreen Scrub-Shrub; PUB/V =
Palustrine Unconsolidated Bottom Mixed with Vegetated Wetland; PUB = Palustrine Unconsolidated
Bottom (includes Unconsolidated Shore); R1EM = Riverine Tidal Emergent Wetland
Broad Deep Gravelly Gum Marshyhope Nanticoke
Wetland Type Creek Creek Branch Branch Creek River
E2EM 33.1 - - - - 47.0
PEM/SS-M 1062.1 421.6 710.1 335.1 822.6 862.6
PEM 187.8 154.8 167.1 3.7 318.6 294.8
Pf 701.2 538.0 172.6 38.8 950.9 908.1
PFO/SS-M 3,917.7 1,228.7 933.3 1,875.3 4,034.6 2,862.0
PFO/EM-M 105.3 - - 7.3 201.1 6.4
PFO-M 1,409.2 3,363.3 3,326.1 1,400.8 2,725.6 3,071.7
PFO-D 4,584.3 3,455.8 1,641.5 1,085.9 9,316.5 6,153.1
PFO-E 1,141.8 1,270.8 1,133.2 105.1 548.1 474.9
PSS-M 749.1 357.6 502.6 182.5 153.1 103.1
PSS-D 534.8 175.6 71.4 137.7 320.5 256.5
PSS-E 952.9 787.7 440.1 272.3 363.6 193.5
PUB/V 41.3 - - - - -
PUB 218.9 106.3 15.4 30.6 36.7 215.0
R1EM 1.8 7.3 - - - 24.4
------------- ---------- ---------- --------- --------- ----------- ----------
Total 15,641.3 11,867.5 9,113.4 5,475.1 19,791.9 15,473.1
46
Table 9. Summary statistics for land use and landcover in subbasins of the Nanticoke watershed.
Acreage of Land Use/Cover Type (percent of total subbasin)
“Natural
Subbasin Developed Agriculture Vegetation”* Water
Broad Creek 6,920 (9%) 38,261 (51%) 29,650 (39%) 976 (1%)
Deep Creek 3,753 (9%) 15,655 (39%) 20,815 (51%) 364 (1%)
Gravelly Branch 1,499 (6%) 7,544 (31%) 15,321 (63%) 142 (<1%)
Gum Branch 1,042 (5%) 9,277 (48%) 8,967 (46%) 45 (<1%)
Marshyhope Creek 2,513 (4%) 33,988 (54%) 25,743 (41%) 124 (<1%)
Nanticoke River 11,480 (12%) 52,820 (57%) 27,533 (30%) 1394 (1%)
*Includes pine plantations and other commercial forests
47
Table 10. Condition of the 100m buffer along streams in each subbasin for four cases: 1)
perennial rivers and streams only (excluding tidal reach), 2) perennials and tidal, 3) perennials,
intermittents, and ditches, 4) perennials including tidal, plus intermittents and ditches, and 5)
perennial streams only (linears including R4SBEx). Buffer data addresses the “land” portion of
the buffer and does not include open water areas.
Percent of Buffer in “Natural Vegetation”
Subbasin Case 1 Case 2 Case 3 Case 4 Case 5
Broad Creek 58% 59% 42% 43% 59%
Deep Creek 65% 64% 48% 48% 65%
Gravelly Branch 80% 80% 61% 61% 81%
Gum Branch 73% 73% 49% 49% 73%
Marshyhope Creek 54% 54% 37% 37% 54%
Nanticoke River 51% 53% 32% 34% 50%
48
Table 11. Condition of the 100m buffer along lakes and ponds for each subbasin.
Subbasin Percent of Buffer in
“Natural Vegetation”
Broad Creek 42%
Deep Creek 41%
Gravelly Branch 57%
Gum Branch 44%
Marshyhope Creek 37%
Nanticoke River 34%
49
Table 12. Condition of the 100m buffer around vegetated wetlands for each subbasin.
Subbasin Percent of Buffer in
“Natural Vegetation”
Broad Creek 40%
Deep Creek 41%
Gravelly Branch 49%
Gum Branch 46%
Marshyhope Creek 28%
Nanticoke River 31%
50
Table 13. Disturbance values for streams and extent of ditching in each subbasin of the
Nanticoke River watershed. Note that totals do not always add up due to computer round-off
procedures.
Miles of Miles of Miles of
Channelized Flowing Dammed Miles of
Stream Perennial Stream Perennial Miles of
Subbasin (% of total)* Streams* (% of total)** Streams** Ditches
Broad Creek 77.3 (59%) 131.1 8.0 (6%) 138.7 251.8
Deep Creek 70.1 (87%) 80.2 3.1 (4%) 82.3 143.9
Gravelly Branch 37.2 (89%) 41.9 3.3 (7%) 45.0 77.0
Gum Branch 35.0 (96%) 36.3 - 36.3 55.2
Marshyhope Creek 110.3 (94%) 117.4 - 117.4 326.8
Nanticoke River 107.6 (75%) 143.1 3.1 (2%) 146.2 272.9
*Excludes tidal reach, impounded segments, and intermittent streams
**Excludes tidal reach and intermittent streams
51
Table 14. Extent of altered wetlands in each subbasin.
Ditched Farmed Impounded Excavated Total
Subbasin Acres Acres Acres Acres Acres
(% of
wetlands)
Broad Creek 8,695 701 199 239 9,834 (63%)
Deep Creek 7,909 538 117 103 8,667 (73%)
Gravelly Branch 4,827 173 61 25 5,086 (56%)
Gum Branch 4,353 39 7 28 4,427 (81%)
Marshyhope Creek 16,168 951 1 38 17,158 (87%)
Nanticoke River 8,203 908 34 232 9,377 (61%)
52
Table 15. Remotely-sensed natural habitat indices for each subbasin in the Delaware portion of
the Nanticoke River watershed. (Note: The River-Stream Corridor Index includes the tidal
reach.)
Remotely-sensed Natural Habitat Indices
Subbasin INC IRSCI200 IWB100 IPLB100 IWE ISWE IDSF ICSL IWD ICNHI
100
Broad Creek 0.40 0.59 0.40 0.42 0.45 1.0 0.06 0.59 0.63 0.36
Deep Creek 0.52 0.64 0.41 0.41 0.43 1.0 0.04 0.87 0.73 0.39
Gravelly Branch 0.63 0.80 0.49 0.57 0.52 1.0 0.07 0.89 0.56 0.51
Gum Branch 0.46 0.73 0.46 0.44 0.35 1.0 0.00 0.96 0.81 0.34
Marshyhope Creek 0.41 0.54 0.28 0.37 0.38* 1.0 0.00 0.94 0.87 0.28
Nanticoke River 0.30 0.53 0.31 0.34 0.36* 1.0 0.02 0.75 0.61 0.27
*Calculations based on part of subbasin where digital soils data were available (37% of
Marshyhope Creek subbasin and 92% of the Nanticoke River subbasin).
53
Wildlife Travel Corridors
Many wetlands and other natural habitats in the Nanticoke River watershed have become
fragmented by human actions. In particular, agricultural conversion of wetlands and neighboring
forests and channelization projects have divided many of these habitats into smaller parcels,
thereby reducing the connectivity among natural habitats. As one aid to help guide wildlife
habitat improvement in the watershed, a map showing some possible places for restoring
connectivity was compiled. Map 22 shows potential sites for restoring connectivity among
wildlife habitats through reforestation of 200m swaths. The designated lands should be open
land (mostly cropland) that are suitable for reforestation (with landowner permission).
Please note that other groups have spent a great deal of time working on “Delmarva Conservation
Corridors” and that individuals interested in wildlife travel corridors and habitat fragmentation
should contact the U.S. Fish and Wildlife Service’s Delaware Bay Estuary Project Office for
information on these corridors (302-653-9152).
54
Conclusions
The findings of this report should be considered preliminary. Field checking should be
conducted to validate the interpretations. The report should, however, serve as a guide to
wetlands in the Nanticoke watershed and to their functions. It is a starting point for resource
planning rather than an endpoint. The characterization serves as one tool to aid in wetland
conservation and watershed management. It should be used with other tools derived from field
observations and other site-specific data.
In the final analysis, a few issues arose that warrant further consideration by the State’s ad hoc
committee for the Nanticoke. These issues are mostly related to the criteria used for identifying
wetlands of potential significance for some functions. For streamflow maintenance, should
ditched portions of headwater wetlands be given the same rating as nonditched portions? In our
assessment, the former were identified as having some potential for this function, while the latter
were designated as having high potential. Should all floodplain wetlands be designated as having
potential for streamflow maintenance or should this potential only be attributed to floodplain
wetlands along low order streams and not to those along mainstem rivers? For nutrient
transformation, based on field investigations, is there a reliable positive correlation between
seasonally flooded and wetter water regimes and amount of organic matter in the soil? Also,
what is the role of seasonally saturated wetlands (“B” water regime; flatwoods) in nutrient
cycling? Presently, only those flatwoods with more than 50 percent of their borders in cropland
were deemed of some significance for nutrient cycling. For shoreline stabilization, pond-fringe
wetlands were included as having high potential for shoreline stabilization. Should they be given
a lower rating? Field checking of seasonally flooded and seasonally flooded/saturated emergent
wetlands should be done to determine if they are marshes or wet meadows. If the former, they
will likely have higher potential as both fish and shellfish habitat and waterfowl habitat than they
were given in this report. Palustrine tidal scrub-shrub/emergent wetlands and tidal
forested/emergent wetlands were designated as having moderate significance for waterfowl and
waterbirds, should their status be upgraded to high potential? All vegetated wetlands were
identified as having at least some potential as habitat for other wildlife. Is the committee still
comfortable with this?
In regard to fragmentation, for this study, we focused on major road crossings and did not treat
small isolated pieces of once larger wetlands that have been chopped up by development as
fragmented. Would it be better to apply this modifier (“fg”) to all potentially fragmented
wetlands? While a four-lane highway (interstate) clearly represents a fragmenting structure, does
a two-lane paved road produce similar consequences? And if so, what about unpaved roads?
Another question arose in applying the fragmentation descriptor to wetland polygons - should
this descriptor be applied to: 1) the entire wetland (main wetland body and the fragmented
section), or 2) only to the fragmented piece(s)? Many large wetlands only had a small portion
that was fragmented.
55
Acknowledgments
This study was funded by the Delaware Department of Natural Resources and Environmental
Control (DNEC), Division of Soil and Water Conservation. Sharon Webb was the project
coordinator for DNREC. Ralph Tiner serving as principal investigator for the Service.
Photointerpretation of wetlands, potential wetland restoration sites, and land use/cover for this
project was performed by John Swords. Gary Doucett mapped the extent of ditches. Wetland
classification of HGM-types following Tiner (2000) was performed by Herb Bergquist who also
processed much of the geospatial data. Bobbi Jo McClain produced the thematic maps and
assisted in data tabulation. Ralph Tiner developed the correlations between wetland
characteristics and wetland functions used to produce the preliminary assessment of wetland
functions, analyzed the data, and prepared the project report. Susan Essig reviewed the final
manuscript for clarity and content.
Amy Jacobs (DNREC) and the wetland group she assembled for reviewed the draft protocols for
correlating wetland characteristics with wetland functions and provided recommendations to
modify the selection criteria. Participants included David Bleil, Katheleen Freeman, Cathy
Wazniak, Mitch Keiler, and Bill Jenkins (Maryland Department of Natural Resource); Julie
LaBranche (Maryland Department of the Environment); Marcia Snyder, Dennis Whigham, and
Don Weller (Smithsonian Environmental Research Center); Matt Perry and Jon Willow (U.S.
Geological Survey); Mark Biddle (DNREC); and Peter Bowman (Delaware Natural Heritage
Program). Mark also provided land use and land cover information from the state’s digital
database. Peggy Emslie (formerly with DNREC) helped initiate this project by identifying the
value of this type of analysis for watershed planning and management.
56
References
Anderson, J.R., E.E. Hardy, J.T. Roach, and R.E. Witmer. 1976. A Land Use and Land Cover
Classification System for Use with Remote Sensor Data. U.S. Geological Survey, Reston, VA.
Geol. Survey Prof. Paper 964.
Askins, R.A., M.J. Philbrick, and D.S. Sugeno. 1987. Relationship between the regional
abundance of forest and the composition of forest bird communities. Biol. Cons. 39: 129-152.
Bowden, W.B. 1987. The biogeochemistry of nitrogen in freshwater wetlands.
Biogeochemistry 4: 313-348.
Brinson, M. M. 1993a. A Hydrogeomorphic Classification for Wetlands. U.S. Army Corps of
Engineers, Washington, DC. Wetlands Research Program, Technical Report WRP-DE-4.
Brinson, M.M. 1993b. Changes in the funcitoning of wetlands along environmental gradients.
Wetlands 13: 65-74.
Buresh, R.J., M.E. Casselman, and W.H. Patrick. 1980. Nitrogen fixation in flooded soil
systems, a review. Advances in Agronomy 33: 149-192.
Carter, V. 1996. Wetland hydrology, water quality, and associated functions. In: J.D. Fretwell,
J.S. Williams, and P.J. Redman (compilers). National Water Summary on Wetland Resources.
U.S. Geological Survey, Reston, VA. Water-Supply Paper 2425. pp. 35-48.
Castelle, A.J., A.W. Johnson, and C. Conolly. 1994. Wetland and stream buffer size
requirements - a review. J. Environ. Qual. 23: 878-882.
Cowardin, L. M., V. Carter, F. C. Golet, and E. T. LaRoe. 1979. Classification of Wetlands and
Deepwater Habitats of the United States. U.S. Fish and Wildlife Service, Washington, DC.
FWS/OBS-79/31.
DeGraaf, R.M. and D.D. Rudis. 1986. New England Wildlife: Habitat, Natural History, and
Distribution. U.S.D.A. Forest Service, Northeastern Forest Expt. Station, Amherst, MA. Gen.
Tech. Rep. NE-108.
DeLaune, R.D., R.R. Boar, C.W. Lindau, and B.A. Kleiss. 1996. Denitrification in bottomland
hardwood wetland soils of the Cache River. Wetlands 16: 309-320.
Desbonnet, A.., P. Pogue, V. Lee, and N. Wolff. 1994. Vegetated B

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Watershed-based Wetland Characterization for Delaware’s
Nanticoke River Watershed:
A Preliminary Assessment Report
U.S. Fish and Wildlife Service
National Wetlands Inventory
Northeast Region
Hadley, MA 01035
September 2001
Watershed-based Wetland Characterization for
Delaware’s Nanticoke River Watershed:
A Preliminary Assessment Report
by
R.W. Tiner, H.C. Bergquist, J.Q. Swords, and B.J. McClain
U.S. Fish and Wildlife Service
Northeast Region
National Wetlands Inventory Program
300 Westgate Center Drive
Hadley, MA 01035
Prepared for the
Delaware Department of Natural Resources and Environmental Control
Division of Soil and Water Conservation
89 Kings Highway
Dover, DE 19901
September 2001
This report should be cited as:
Tiner, R.W., H.C. Bergquist, J.Q. Swords, and B.J. McClain. 2001. Watershed-based Wetland
Characterization for Delaware’s Nanticoke River Watershed: A Preliminary Assessment Report.
U.S. Fish & Wildlife Service, National Wetlands Inventory (NWI) Program, Northeast Region,
Hadley, MA. Prepared for the Delaware Department of Natural Resources and Environmental
Control, Division of Soil and Water Conservation, Dover, DE. NWI technical report. 89 pp.
plus 22 maps.
Table of Contents
Page
Introduction 1
Study Area 1
Methods 2
Improved Baseline NWI Data 2
Expanded NWI Data 3
Preliminary Assessment of Wetland Functions 4
Wetland Restoration Site Inventory 6
Ditch Inventory 6
Water Resource Buffer Analysis 7
Overall Ecological Condition of the Watershed 8
General Scope and Limitations of the Study 14
Appropriate Use of this Report 18
Rationale for Preliminary Functional Assessments 19
Surface Water Detention 19
Streamflow Maintenance 20
Nutrient Transformation 20
Retention of Sediments and Other Particulates 23
Shoreline Stabilization 23
Provision of Fish and Shellfish Habitat 23
Provision of Waterfowl and Waterbird Habitat 25
Provision of Other Wildlife Habitat 26
Conservation of Biodiversity 29
Results 30
Wetland Classification and Inventory 30
Wetlands by NWI Types 30
Hydrogeomorphic-type Wetlands 33
Maps 36
Summary of Preliminary Assessment of Wetland Functions 37
Potential Wetland Restoration Sites 39
Extent of Ditching 41
Water Resource Buffer Analysis 41
Natural Habitat Integrity Indices 42
Values for the Entire Watershed 42
Summaries for Each Subbasin 43
Wildlife Travel Corridors 52
Conclusions 53
Acknowledgments 54
References 55
Appendices 59
1. Keys to Waterbody Type and Hydrogeomorphic-type Wetland
Descriptors for
for U.S. Waters and Wetlands (Operational Draft)
60
2. Preliminary Functional Assessment Findings for each Subbasin
83
Thematic Maps in separate folder on the CD
Introduction
Today there is great interest in managing wetland resources from a watershed standpoint or
landscape perspective. Wetland managers need information on a variety of topics including the
location and type of existing wetlands, wetland functions, potential wetland restoration sites, and
the overall condition of natural habitat in the watershed. The U.S. Fish and Wildlife Service’s
National Wetlands Inventory Program has developed products that expand the use of its
conventional maps and digital products to aid in resource management. The Delaware
Department of Natural Resources and Environmental Control (DNREC) is attempting to reduce
nonpoint source pollution impacts in the Nanticoke watershed and wanted the above information
for the Delaware portion of the Nanticoke River watershed. This information would be used to
help improve water quality and management and conservation of fish and wildlife habitat in
wetlands, streams, riparian areas, and uplands in Delaware. Similar work has recently been
completed for the Maryland portion of the watershed (Tiner et al. 2000). In the future, both
efforts may be combined into a single report.
The DNREC, through its Division of Soil and Water Conservation, provided funding to the
Service to produce watershed-wide information on wetlands, streams, riparian areas, and
uplands. The following products were scheduled for production: 1) a wetland characterization
report for the Delaware portion of the Nanticoke River watershed, 2) a set of GIS-produced maps
showing wetlands and highlighting wetlands of potential significance for performing various
functions, 3) edited and updated digital databases, 4) updated NWI maps for 11 quads, and 5) a
summary of the remotely-sensed natural habitat (ecological) integrity indices for the Nanticoke
River watershed and its subbasins.
The report is organized into the following sections: Study Area, Methods, General Scope and
Limitations of the Study, Appropriate Use of this Report, Rationale for Preliminary Functional
Assessments, Results, Conclusions, Acknowledgments, and References. Two appendices provide
keys to hydrogeomorphic wetland classification and the functional assessment findings for
subbasins. Thematic maps are contained in a separate folder on the CD version of this report.
Study Area
The study area is the Delaware portion of the Nanticoke River watershed. This roughly 490-
square mile drainage area occurs in western Delaware along its border with Maryland. It
represents about 25 percent of the state of Delaware. This watershed contains the six subbasins:
Broad Creek, Deep Creek, Gravelly Branch, Gum Branch, Marshyhope Creek, and the Nanticoke
River. The watershed encompasses parts of Sussex, Kent, and New Castle Counties. It appears
on the following 14 quads: Seaford West, Sharptown, Hebron, Hickman, Greenwood, Ellendale,
Seaford East, Georgetown, Laurel, Trap Pond, Delmar, Pittsville, Burrsville, and Harrington.
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Methods
The purpose of the project was to produce new information to assist Delaware wetland managers
in wetland planning and evaluation at the watershed level (see section on Appropriate Use of this
Report). The foundation of this project was construction of a fairly comprehensive, geospatial
wetland database. The existing wetland digital data for Delaware included the National
Wetlands Inventory (NWI) data (based on 1:24,000 maps derived from mostly early 1980s-1:58K
color infrared photography), the State’s wetland data (based on digital orthophoto quarter-quads
produced from spring 1992-1:40K color infrared photographs), and the State’s land use and land
cover data (mid-1990s data). The NWI data were used as the foundation since they are part of a
national database and match up well with other national digital data, especially hydrology data
from the U.S. Geological Survey. The State data were used as collateral data to improve the
delineation of wetlands in the NWI database. Updated NWI data and land use/land cover data
were derived through interpreting spring 1998-1:40K black and white photography.
The NWI database was also expanded to include hydrogeomorphic-type attributes for all mapped
wetlands and waterbodies, an inventory of ditches, an inventory of potential wetland restoration
sites, and geospatial data on land use and land cover in both watersheds. The information
contained within the database was then used to produce summary statistics, thematic maps, and a
wetland characterization report for the watersheds. The characterization included: 1) a summary
of the extent and distribution of wetland types (by NWI type and hydrogeomorphic type), 2) a
preliminary assessment of wetland functions for each watershed, 3) an inventory of potential
wetland restoration sites, 4) a description of the condition of wetland and waterbody buffers, 5)
an overall assessment of natural habitat for the watershed, and 6) an assessment of the extent of
ditching. The following discussion describes procedures used to produce this information. The
report summarizes the study findings for each watershed. These results should be considered
preliminary as they have not been subject to agency or field review.
Improved Baseline NWI Data
The first step in the project was updating the NWI maps and digital database, since these data
would be used for the analysis of wetland functions. The existing NWI dataset was both dated
(derived from early 1980s photography) and conservative (e.g., many flatwoods were not
mapped). We updated the NWI digital data using a digital transfer scope. This equipment
allowed integration of existing digital wetland and hydric soil data and editing of the digital data
through photointerpretation of spring 1998-1:40K black-and-white aerial photography. Digital
data used to assist in updating were: 1) Delaware wetlands produced by the State from 1992
photography, and 2) hydric soil data from the U.S.D.A. Natural Resources Conservation
Service’s (NRCS) soil surveys for Kent and Sussex Counties. Utilizing hydric soils digital data
to help expand the mapping of flatwood wetlands may have led to some errors of commission
(i.e., inclusion of upland forests in flatwood polygons), since these are among the most difficult
wetlands to photointerpret (Tiner 1999). These wetlands tended to be classified as a seasonally
saturated forested wetland of some kind (broad-leaved deciduous, needle-leaved evergreen, or
mixed; NWI codes such as PFO1B, PFO4B, PFO1/4B, and PFO4/1B). For the original NWI
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mapping, most of the mapped wet flatwoods were labelled as temporarily flooded, since ponding
was observed in a few places. Since the 1980s, more work has been done in the Coastal Plain
and the hydrology of wet flatwoods has been determined to be best described as “seasonally
saturated.” This is because high water tables are typical in winter and early spring, with little
standing water present. Locally these wetlands are often called “winter wet woods.” The
classifications of these flatwoods were revised to reflect a seasonally saturated condition (i.e.,
applied the “B” or “saturated” water regime modifier). The NRCS data for hydric soils and
Delaware wetland data were mainly used as collateral sources to aid in flatwood wetland
identification and the former also for assisting in classification of floodplain wetlands.
Expanded NWI Data
Once a more complete inventory of wetlands was created, the NWI database was further
expanded by adding hydrogeomorphic-type information to each mapped wetland. Landscape
position, landform, water flow path, and other descriptors were applied to all wetlands in the
NWI digital database by merging NWI data with on-line U.S. Geological Survey topographic
maps and consulting aerial photography where necessary (see Tiner 2000; Appendix of this
report for keys to these descriptors).
Landscape position defines the relationship between a wetland and an adjacent waterbody, if
present. Four landscape positions are relevant to the study watersheds: 1) lotic (along freshwater
rivers and streams), 2) lentic (in lakes, reservoirs, and their basins), 3) terrene (isolated,
headwater, or fragments of former isolated or headwater wetlands that are now connected to
downslope wetlands via drainage ditches), and 4) estuarine (in estuaries). Lotic wetlands are
further separated by river and stream gradients as high (e.g., shallow mountain streams on steep
slopes - not present in the study areas), middle (e.g., streams with moderate slopes - not present
in the study areas), low (e.g., mainstem rivers with considerable floodplain development as in the
Nanticoke watershed), and tidal (i.e., under the influence of the tides). "Rivers" are separated
from "streams" solely on the basis of channel width: watercourses mapped as linear (one-line)
features on an NWI map and a U.S. Geological Survey topographic map were designated as
streams, whereas two-lined channels (polygonal features) on these maps were classified as rivers.
Total river-stream length was determined by running a centerline through all river polygons and
adding this mileage to the miles of linear streams.
Landform is the physical form of a wetland or the predominant land mass on which it occurs
(e.g., floodplain or interfluve). Six types are recognized in the study areas: basin, interfluve, flat,
floodplain, fringe, and island (see Table 1 for definitions). The Johnston soil was the only soil
series in the watershed that was associated with floodplain wetlands.
Additional modifiers were assigned to indicate water flow paths associated with wetlands:
bidirectional, throughflow, inflow, outflow, or isolated. Bidirectional flow is two-way flow
either related to tidal influence or water level fluctuations in isolated lakes and impoundments.
Throughflow wetlands have either a watercourse or another type of wetland above and below it,
so water flows through the subject wetland. All lotic wetlands are throughflow types. Inflow
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wetlands are sinks where no outlets exist, yet water is entering via a stream or river or an upslope
wetland. Outflow wetlands have water leaving them and moving downstream via a watercourse
or a slope wetland. Isolated wetlands are essentially closed depressions or flats where water
comes from surface water runoff and/or ground water discharge.
Other descriptors applied to mapped wetlands include headwater, drainage-divide, and
fragmented. Headwater wetlands are sources of streams or wetlands along first order (perennial)
streams. They include wetlands connected to first order streams by ditches. The latter wetlands
were also labeled with a ditched modifier. Many such wetlands are remnants of once larger
interfluve wetlands that drained directly into streams. Drainage-divide wetlands are wetlands
that occur in more than one watershed or subbasin, straddling the defined watershed boundary
line between a watershed or subbasin and a neighboring one. We identified pieces of wetlands
separated by major highways (federal and state roads) as fragmented wetlands. This is a first step
in addressing the issue of fragmentation which is quite complex and beyond the scope of our
work. For example, we did not apply the descriptor to wetlands that were simply reduced in size
due to land use practices. The listing of fragmented wetlands is extremely conservative.
For open water habitats such as the ocean, estuaries, lakes, and ponds, we also applied additional
descriptors following Tiner (2000). For the study watersheds, such classification was mainly
relevant for ponds.
Preliminary Assessment of Wetland Functions
After improving and enhancing the NWI digital database, several analyses were performed to
produce a preliminary assessment of wetland functions for the watershed. Nine wetland
functions were evaluated: 1) surface water detention, 2) streamflow maintenance, 3) nutrient
transformation, 4) sediment and other particulate retention, 5) shoreline stabilization, 6) fish and
shellfish habitat, 7) waterfowl and waterbird habitat, 8) other wildlife habitat, and 9) biodiversity.
The rationale for correlating wetland characteristics with wetland functions is described in a
later section of this report. After running the analyses, a series of maps for watershed were
generated to highlight wetland types that may perform these functions at high or other significant
levels. Statistics and topical maps for the study area were generated by ArcView software.
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Table 1. Definitions and examples of landform types (Tiner 2000).
Landform Type General Definition Examples
Basin* a depressional (concave) landform lakefill bogs; wetlands in the
saddle between two
hills; wetlands in closed or
open depressions, including
narrow stream valleys
Slope a landform extending uphill (on a slope) seepage wetlands on
hillside; wetlands along
drainageways or mountain
streams on slopes
Flat* a relatively level landform, often on wetlands on flat areas
broad level landscapes with high seasonal ground-water
levels; wetlands on
terraces along rivers/streams;
wetlands on hillside benches;
wetlands at toes of slopes
Floodplain a broad, generally flat landform wetlands on alluvium;
occurring on a landscape shaped by bottomland swamps
fluvial or riverine processes
Interfluve a broad level to imperceptibly flatwood wetlands on coastal
depressional poorly drained landform or glaciolacustrine plains
occurring between two drainage systems
(on interstream divides)
Fringe a landform occurring along a flowing or buttonbush swamps; aquatic
standing waterbody (lake, river, stream) beds; semipermanently
and typically subject to permanent, flooded marshes; salt and
semipermanent flooding or frequent tidal brackish marshes
flooding; including wetlands within stream
or river channels and estuarine wetlands
with unrestricted tidal flow
Island a landform completely surrounded by deltaic and insular wetlands;
water (including deltas) floating bog islands
*May be applied as sub-landforms within the Interfluve and Floodplain landforms.
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Wetland Restoration Site Inventory
Wetland restoration efforts have been accelerating over the past decade throughout the country.
Much of the work done to date has been on an ad hoc basis without knowledge of a broader
universe of potential sites. In many areas of the country, site selection for wetland restoration has
simply been driven by opportunities and not by a holistic view of watersheds and wetland
resources. Recently, the State of Massachusetts initiated a watershed-based restoration process,
where potential wetland restoration sites are identified throughout an entire watershed, then
matched with locations of various “watershed-deficits” (e.g., flooding problems, areas of
degraded water quality, and lack of connectivity between significant fish and wildlife habitats) in
an effort to promote wetland restoration where the greatest public good can be gained. Such
work provides agencies, organizations, and others interested in wetland restoration with a wide
selection of potential sites. The Delaware Department of Natural Resources and Environmental
Control is interested in this process, so we identified potential wetland restoration sites for the
subject watershed.
An inventory of potential wetland restoration sites was performed by examining aerial photos,
hydric soil information, and existing wetland data (e.g., for farmed wetlands, wetlands
experiencing possible hydrologic restrictions, plus diked, ditched, and excavated vegetated
wetlands). Two major types of wetland restoration sites were identified: Type 1 sites - former
vegetated wetlands that appear suitable for restoration, and Type 2 sites - existing vegetated
wetlands whose functions appear to be significantly impaired by ditching, excavation, and
impoundment. Type 1 restoration sites included former wetlands that were filled and that did not
have buildings or other facilities constructed on them, farmed wetlands, and vegetated wetlands
that were converted to deepwater habitats such as impounded lakes. Farmed wetlands may
technically be considered Type 2 candidates, but since their condition is impaired to the point
that they only minimally meet the definition of wetland in the subject areas, they were considered
Type 1 sites. Type 2 restoration sites are mostly existing vegetated wetlands that are impounded,
excavated, partly drained (ditched), and potentially tidally restricted, but also include shallow
ponds constructed on hydric soils. For ditched wetlands, no attempt was made to evaluate the
scope and effect of ditching as this requires field-based assessment. One, however, might
consider the degree of ditching as observed on the map showing the extent of ditching as a way
of assessing the relative impact of ditching on various wetlands.
Ditch Inventory
To determine the extent of ditches in the watershed, we began with the digital hydrology
coverage from the U.S. Geological Survey 1:24K map series (digital line graphs - DLGs). This
coverage was reviewed to help separate “natural streams” from “ditches” and formed the
foundation for the “ditch” data layer. To create an up-to-date “ditch” coverage,
photointerpretation of 1998 aerial photography1 was performed using a digital transfer scope.
1For the Nanticoke watershed, initial mapping of ditches was accomplished by
photointerpreting 1989 photos since the 1998 photos were not available until later in the project.
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Ditches were separated from channelized and natural streams. Data presented include number of
ditch miles and the density of ditches per study watershed.
Water Resource Buffer Analysis
A 100m-wide (328 feet) stream buffer has been reported to be important for neotropical migrant
bird species in the Mid-Atlantic region (Keller et al. 1993) and streamside vegetation providing
canopy coverage over streams is important for lowering stream temperatures and moderating
daily fluctuations that is vital to providing suitable habitat for certain fish species (e.g., trout).
Review of the literature on buffers suggests wider buffers, such as 500m (1,640 feet) or more, for
certain species of wildlife (e.g., Kilgo et al. 1998 for southern bottomland hardwood stream
corridors). Semlitsch and Jensen (2001) emphasize that “wetland buffers” should be better
described as “core habitat” for semiaquatic species and they urge that such areas be protected and
managed as vital habitats. They found that 95 percent of the breeding population of mole
salamanders lived in the adjacent forest within 164m (538 feet) of their vernal pool wetland. An
interesting article by Finlay and Houlahan (1996) indicates that land use practices around
wetlands may be as important to wildlife as the size of the wetland itself. They reported that
removing 20 percent of the forest within 1000m (3,281 feet) of a wetland may have the same
effect on species as destroying 50 percent of the wetland. For literature reviews of wetland and
stream buffers, see Castelle et al. (1994) and Desbonnet et al. (1994).
The condition of these buffers is also significant for locating possible sources of water quality
degradation. Wooded corridors should provide the best protection, while developed corridors
(e.g., urban or agriculture) should contribute to substantial water quality and aquatic habitat
deterioration. Since wetland and waterbody buffers are important features that relate to the
quality of these aquatic habitats, we performed an analysis of the condition of these buffers. This
information was also used in evaluating the overall ecological condition or the condition of
natural habitats for each watershed.
These data were updated with the 1998 photos to create a 1998-era database for ditches.
A 100m-wide buffer was selected for analysis. The buffer was positioned around various water
resource features, i.e., wetlands, lakes, ponds, streams, and ditches. To evaluate the condition of
the buffer, we created a land use/land cover data layer by combining existing digital data with
new photointerpretation. The state’s existing digital data on land use/land cover was used as the
foundation. These data were updated by interpreting 1998 aerial photography (1:40,000 black
and white) using a digital transfer scope. We used the Anderson et al. (1976) land use/land cover
classification system and classified upland habitats to level two in this system. The following
categories were among those identified: developed land (e.g., residential, commercial, industrial,
transportation/communication, utilities, other, institutional/government, and recreational),
agricultural land (cropland, pasture, orchards, nurseries, horticulture, feedlots, and holding areas),
forests (deciduous, evergreen, mixed, and clear-cut), wetlands (from NWI data), and transitional
8
land (moving toward some type of development or agricultural use, but future status unknown).
Data layers were constructed for the entire “land” area of each watershed so that information
could also be used for assessing their overall ecological condition. Buffer analysis is one of the
key landscape variables used to judge this condition. Data on buffers were reported for various
water resource features: perennial nontidal rivers and streams, wetlands, ponds and lakes
(impoundments), and a few combinations of perennial rivers and streams, intermittent streams,
and ditches.
Overall Ecological Condition of the Watershed
There are many ways to assess land use/cover changes and habitat disturbances. The health and
ecological condition of a watershed may be assessed by considering such features as the integrity
of the lotic wetlands and riparian forests (upland forests along streams), the percent of land uses
that may adversely affect water quality in the watershed (% urban, % agriculture, % mining, etc.),
the actual water quality, the percent of forest in the watershed, and the number of dams on
streams, for example. Recent work on assessing the condition of watersheds has been done in
the Pacific Northwest to address concerns for salmon (Wissmar et al. 1994; Naiman et al. 1992).
A Wisconsin study by Wang et al. (1997) found that instream habitat quality declined when
agricultural land use in a watershed exceeded 50 percent, while when only 10-20 percent of the
watershed was urbanized, severe degradation occurred.
To assess the overall ecological condition of watersheds, the Northeast Region of the U.S. Fish
and Wildlife Service has developed a set of largely remotely-sensed “natural habitat integrity”
indices (formerly referred to as “ecological integrity indices”). The variables for these indices are
derived through air photointerpretation and/or satellite image processing coupled with knowledge
of the historical extent of wetlands and open waterbodies. They are coarse-filter variables for
assessing the overall condition of watersheds. They are intended to augment, not supplant, other
more rigorous, fine-filter approaches for describing the ecological condition of watersheds (e.g.,
indices of biological integrity for macroinvertebrates and fish and the extent and distribution of
invasive species) and for examining relationships between human impacts and the natural world.
The natural habitat integrity indices can be used to develop “habitat condition profiles” for
individual watersheds of varying scales (i.e., subbasins to major watersheds). Indices can be
used for comparative analysis of subbasins within watersheds and to compare one watershed with
another. They may also serve as one set of statistics for reporting on the “state-of-the-environment”
by government agencies and environmental organizations or for evaluating the
historic trends in the extent of natural habitats.
The indices are rapid-assessment types that allow for frequent updating (e.g., every 5-10 years).
They may be used to assess and monitor the amount of “natural habitat” compared to the amount
of disturbed aquatic habitat (e.g., channelized streams, partly drained wetlands, and impounded
wetlands) or developed habitat (e.g., cropland, grazed meadows, mined lands, suburban
development, and urbanized land). The index variables include features important to natural
resource managers attempting to lessen the impact of human development on the environment.
The indices may also be compared with other environmental quality metrics such as indices of
9
biological integrity for fish and/or macroinvertebrates or water quality parameters. If significant
correlations can be found, they may aid in projecting a “carrying capacity” or threshold for
development for individual subbasins. This would require further classification of the developed
land category into various agricultural types and urban/suburban types which is easily
accomplished.
Prior to initiating this project, a total of nine indices were developed for nontidal areas. We split
one of them into two indices for a new total of ten indices. All of them, in one way or another,
represent habitat condition in a watershed. Six indices address natural habitat extent (i.e., the
amount of natural habitat occurring in the watershed and along wetlands and waterbodies):
natural cover, river-stream corridor integrity, vegetated wetland buffer integrity, pond and lake
buffer integrity, wetland extent, and standing waterbody extent. Use of terms like “natural
habitat” and “natural vegetation” have stirred much debate, yet despite this, we feel that they are
useful for discussing the effects of human activities on the environment. For purposes of this
study, “natural habitats” are defined as areas where significant human activity is limited to nature
observation, hunting, fishing, or timber harvest, and where vegetation is allowed to grow for
many years without annual introduction of chemicals or annual harvesting of vegetation or fruits
and berries for commercial purposes. Natural habitats may be managed, yet are not intensively
managed or subjected to heavy human traffic. They are places where wetland and terrestrial
wildlife find food, shelter, and water. In other words, they are essentially plant communities
represented by “natural” vegetation such as forests, meadows, and shrub thickets. They are not
developed sites (e.g., impervious surfaces, lawns, turf, cropland, pastures, or mowed hayfields).
Managed forests are included as natural habitat, whereas orchards and vineyards are not.
“Natural habitat” therefore includes habitats ranging from pristine woodlands and wetlands to
wetlands now colonized by invasive species (e.g., Phragmites australis or Lythrum salicaria) or
commercial forests planted with loblolly pine. Natural vegetation does not imply that substantial
groundcover must be present, but simply that the communities reflect the vegetation that is
capable of growth and reproduction in accordance with site characteristics (e.g., sand dunes and
beaches).
Three indices emphasize human-induced alterations to streams and wetlands. These “stream and
wetland disturbance indices” address dammed stream flowage, channelized stream flowage, and
wetland disturbance. The nine specific indices may be combined into a single, composite index
called “remotely-sensed natural habitat integrity index” for the watershed. All indices have a
maximum value of 1.0 and a minimum value of zero. For the habitat extent indices, the higher
the value, the more habitat available. For the disturbance indices, the higher the value, the more
disturbance. For the remotely-sensed natural habitat integrity index, all indices are weighted,
with the disturbance indices subtracted from the habitat extent indices to yield an overall “natural
habitat integrity” score for the watershed.
Data for these indices came from the improved NWI digital database and a newly created land
use/land cover database for the two watersheds. The data were derived primarily through aerial
photointerpretation with review of existing information. The indices do not include certain
qualitative information on the condition of the existing habitats (habitat quality) as reflected by
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the presence, absence, or abundance of invasive species or by fragmentation of forests, for
example. It may be possible to add such data in the future, especially for the latter. Another
consideration would be establishment of minimum size thresholds to determine what constitutes
a viable “natural habitat” for analysis (e.g., 0.04 hectare/0.1 acre patch of forest or 0.4 hectare/1
acre minimum?). Other indices may also need to be developed to aid in water quality
assessments (e.g., index of ditching density for agricultural and silvicultural lands). The nine
indices are summarized below.
Habitat Extent Indices
These indices have been developed to provide some perspective on the amount of natural
vegetation that occurs in a watershed. The following areas are emphasized: the entire watershed,
stream and river corridors, vegetated wetlands and their buffers, and pond and lake buffers. The
extent of standing waterbodies is also included to provide information on the amount of aquatic
habitat in the watershed. Each index is briefly described below.
The Natural Cover Index (INC) is derived from a simple percentage of the subbasin that is
wooded (e.g., upland forests or shrub thickets and forested or scrub-shrub wetlands) and
“natural” open land (e.g., emergent wetlands or “old fields;” but not cropland, hayfields, lawns,
turf, or pastures). These areas are lands supporting “natural vegetation” and they exclude open
water of ponds, rivers, lakes, streams, and coastal bays.
INC = ANV/AW , where ANV (area in natural vegetation) equals the area of the watershed’s
land surface in “natural” vegetation and AW is the area of "watershed" excluding open
water.
The River-Stream Corridor Integrity Index (IRSCI) is derived by considering the condition of the
stream corridors around perennial rivers and streams2:
IRSCI = AVC/ATC , where AVC (vegetated river-stream corridor area) is the area of the
river-stream corridor that is colonized by “natural vegetation” and ATC (total river-stream
corridor area) is the total area of the river-stream corridor.
2Including streams designated as seasonally flooded/saturated intermittent streams (i.e.,
R4SBEx) which flow for long periods during the year, but not year-round. Such streams were
identified on the source data (U.S.Geological Survey DLGs) as perennial, but based on our field
experiences and those of Amy Jacobs (DNREC) it was agreed that these streams are not
perennial.
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The width of the river-stream corridor may be varied to suit project goals, but for this project, a
200-meter (656 feet) corridor (100m on each side of the river or stream) was evaluated. To
compute total river-stream length, the centerlines of river polygons are used to derive river length
and this was added to stream length (from linear data). Also note that these corridors include
impounded sections of rivers and streams, so that a continuous river or stream corridor is
evaluated. The centerlines of these polygons were used to determine stream length. For this
watershed, the index was applied to nontidal rivers for assessing the composite natural habitat
integrity index. When the entire Nanticoke River watershed is evaluated in the future, the index
should include tidal portions of the river as well.
The Wetland Buffer Integrity Index (IWB) is a measure of the condition of wetland buffers within
a specified distance (e.g., 100m) of mapped vegetated wetlands for the entire watershed:
IWB = AVB/ATB , where AVB (area of vegetated buffer) is the area of the buffer zone that is
in natural vegetation cover and ATB is the total area of the buffer zone.
This buffer is drawn around existing vegetated wetlands. While the buffer zone may include
open water, the buffer index will focus on land areas that may support free-standing vegetation.
Note that for the analysis of the Maryland portion of the Nanticoke River watershed, the wetland
buffers were included with the pond and lake buffers in an index called Wetland and Waterbody
Buffer Index (IWWB). Buffer width can be varied according to regional needs and conditions. For
the Nanticoke River watershed analysis, a 100m buffer was examined.
The Pond and Lake Buffer Integrity Index (IPLB) addresses the status of buffers of a specified
width around these standing waterbodies (excluding in-stream impoundments that are included in
the river-stream corridor integrity index):
IPLB = AVB/ATB , where AVB (area of vegetated buffer) is the area of the buffer zone that
is in natural vegetation cover and ATB is the total area of the buffer zone.
See comments under the wetland buffer integrity index above. Ponds are shallow waterbodies
mapped as palustrine unconsolidated bottoms and unconsolidated shores by NWI. Vegetated
ponds are mapped as a vegetated wetland type and their buffers are not included in this analysis,
but instead are evaluated as wetland buffers. For the Nanticoke River watershed analysis, a
100m buffer was examined.
The Wetland Extent Index (IWE) compares the current extent of vegetated wetlands (excluding
nonvegetated, open-water wetlands) to the estimated historic extent.
IWE = ACW/AHW , where ACW is the current area of vegetated wetland in the watershed
and AHW is the historic vegetated wetland area in the watershed.
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The IWE is an approximation of the extent of the original wetland acreage remaining in the
watershed. Farmed wetlands are included where cultivation is during droughts only, since they
are likely to support “natural vegetation” during normal and wet years. Where farmed wetlands
are cultivated more or less annually such as in much of the Northeast region, they are not
included in the area of vegetated wetland, since they lack “natural vegetation” in most years and
only minimally function as wetland. For the Nanticoke watershed, hydric soils data are available
for the Kent and Sussex Counties portion of the watershed and were used to calculate the wetland
extent index for the watershed.
The Standing Waterbody Extent Index (ISWE) addresses the current extent of standing fresh
waterbodies (e.g., lakes, reservoirs, and open-water wetlands - ponds) in a watershed relative to
the historic area of such features.
ISWE = ACSW/AHSW , where ACSW is the current standing waterbody area and AHSW is the
historic standing waterbody area in the watershed.
Since the Nanticoke watershed has experienced a net gain in ponds and impoundments over time,
the ISWE value is 1.0+ which indicates a gain in this aquatic resource with no specific calculations
necessary. A value of 1.0 was used for determining the composite natural habitat integrity index
for the watershed.
Stream and Wetland Disturbance Indices
A set of three indices have been developed to address alterations to streams and wetlands. For
these indices, a value of 1.0 is assigned when all of the streams or existing wetlands have been
modified.
The Dammed Stream Flowage Index (IDSF) highlights the direct impact of damming on rivers and
streams in a watershed.
IDSF = LDS/LTS , where LDS is the length of perennial streams impounded by dams
(combined pool length) and LTS is the total length of perennial streams in the watershed
(including the length of in-stream pools).
Note that the total stream length used for this index will be greater than that used in the
channelized stream length index, since the latter emphasizes existing streams and excludes the
length of dammed segments. See footnote 2. Also note that this index was not applied to the full
length of the Nanticoke River, but only to linear streams. In the future, this index should be
expanded to include the entire river-stream length (i.e., the Dammed River-Stream Flowage
Index).
The Channelized Stream Length Index (ICSL) is a measure of the extent of channelization of
streams within a watershed.
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ICSL = LCS/LTS , where LCS is the channelized stream length and LTS is the total stream
length for the watershed.
Since this index addresses channelization of existing streams, it focuses on the linear streams.
The index will usually emphasize perennial streams as it does for the Nanticoke River study, but
could include intermittent streams, if desirable. See footnote 2. The total stream length does not
include the length of: 1) artificial ditches excavated in farmfields and forests, 2) dammed
sections of streams, and 3) polygonal portions of rivers.
The Wetland Disturbance Index (IWD) focuses on alterations within existing wetlands. As such,
it is a measure of the extent of existing wetlands that are diked/impounded, ditched, excavated,
or farmed:
IWD = ADW/ATW , where ADW is the area of disturbed or altered wetlands and ATW is the
total wetland area in the watershed.
Wetlands are represented by both vegetated and nonvegetated (e.g., shallow ponds) types and
also include natural and created wetlands. Since the focus of our analysis is on “natural habitat,”
diked or excavated wetlands (or portions thereof) are viewed as an adverse action. We
recognize, however, that many such wetlands may serve as valuable wildlife habitats (e.g.,
waterfowl impoundments), yet they remain classified as disturbed wetlands.
Composite Habitat Index for the Watershed
The Composite Natural Habitat Integrity Index (ICNHI) is a combination of the preceding indices.
It seeks to express the overall condition of a watershed in terms of its potential ecological
integrity or the relative intactness of “natural” plant communities and waterbodies, without
reference to specific qualitative differences among these communities and waters. Variations of
ICNHI may be derived by considering buffer zones of different widths around wetlands and other
aquatic habitats (e.g., ICNHI 100 or ICNHI 200) and by applying different weights to individual indices
or by separating or aggregating various indices (e.g., stream corridor integrity index, river
corridor integrity index, or river-stream corridor integrity index).
For the analysis of Delaware’s Nanticoke River watershed, the following formula was used to
determine this composite index:
ICNHI 100 = (0.5 x INC) + (0.125 x IRSCI200) + (0.125 x IWB100) + (0.05 x IPLB100)+ (0.1 x IWE), + (0.1 x
ISWE) - (0.1 x IDSF) - (0.1 x ICSL) - (0.1 x IWD)
where the condition of the 100m buffer is used throughout. (Note: With this size buffer, the
river/stream corridor width becomes 200m.)
While the weighting of the indices may be debatable, the results of this analysis are comparable
among subbasins. The same weighting scheme must be used whenever comparisons of this
index are made between watersheds or major portions of watersheds, such as the Maryland
portion of the Nanticoke to the Delaware portion of the Nanticoke watershed.3
Data for Natural Habitat Integrity Indices
The data used to compile these indices come from a few sources. Primary data sources included
the enhanced NWI digital data layer, U.S.D.A. Natural Resources Conservation Service’s soil
data, the State’s land use/land cover data for the Nanticoke watershed. and the U.S. Geological
Survey digital line graphs (DLGs). We updated the original NWI data to the year 1998 through
photointerpretation using a digital transfer scope. Spring 1998-1:40,000 black and white
photography was used for updating. This update focused on major areas of land use change and,
therefore, does not represent a comprehensive revision. We emphasized changes between
“natural” habitat, agriculture, and developed land. We added coding for larger levees along
channelized streams, but did not recode all levees. Many levees had been classified as
agricultural land by the State. Stream data based on 1:24,000 topographic maps were expanded
to include a more complete assessment of ditches and channelized stream segments. We also
changed the classification of many headwater stream segments draining interfluve wetlands from
perennial to intermittent (seasonally flooded/saturated = “E”) since such streams do not flow
year-round (confirmed by Amy Jacobs, Delaware Department of Natural Resources and
Environmental Control)
General Scope and Limitations of the Study
Wetland Inventory and Digital Database
The wetlands inventory and digital database are an update of the original NWI database and serve
as the foundation for a preliminary watershed characterization. One must, however, recognize
the limitations of any wetland mapping effort derived mainly through photointerpretation
techniques (see Tiner 1997, 1999 for details). For example, use of spring aerial photography for
wetland mapping precludes identification of freshwater aquatic beds. Such areas are included
within areas mapped as open water (e.g, lacustrine and palustrine unconsolidated bottom)
because vegetation is not developed so they appear as water on the aerial photographs. Also
drier-end wetlands such as seasonally saturated and temporarily flooded wetlands are often
difficult to separate from nonwetlands through photointerpretation.
3For the Maryland portion of the Nanticoke watershed, an earlier version of the formula was
used, so results are not equivalent, although they should be similar. Additional analysis is
required to make more valid comparisons.
14
Although not a prime purpose of the study, we identified some wetlands that were subjected to
fragmentation. Our approach was an extremely conservative one, focusing on wetlands separated
by major roads. We recognize that many small wetlands are actually the remaining fragments
(remnants) of once large wetlands and may also be considered fragments. However, for this
15
report, we applied the fragmented descriptor ("fg") only to wetlands that were divided into two or
more units by major roads which likely disrupted the hydrology and created an increased risk for
wildlife crossing. Moreover, the fragmented descriptor was only applied to pieces of wetlands
separated by major roads, hence the results are extremely conservative. Fragmentation in this
context, therefore, did not address the issue from the broad landscape perspective. To do so
requires analysis beyond the scope of our study. For readers with an interest in fragmentation,
the overall pattern of habitat fragmentation can be seen by looking at Map 22, while the pattern
of wetland fragmentation may be observed on one of the wetland maps prepared for this study
(i.e., Maps 1-4).
Preliminary Assessment of Wetland Functions
At the outset, it is important to emphasize that this functional assessment is a preliminary one
based on wetland characteristics interpreted through remote sensing and using the best
professional judgment of the senior author and an ad hoc group of wetland specialists assembled
by the DNREC.4 Wetlands believed to be providing potentially high or other significant levels of
performance for a particular function were highlighted. As the focus of this report is on
wetlands, an assessment of deepwater habitats (e.g., lakes, rivers, and estuaries) for providing the
listed functions was not done (e.g., it is rather obvious that such areas provide significant
functions like fish habitat). Also, no attempt was made to produce a more qualitative ranking for
each function or for each wetland based on multiple functions as this would require more input
from others and more data, well beyond the scope of this study. For a technical review of
wetland functions, see Mitsch and Gosselink (2000) and for a broad overview, see Tiner (1985;
1998).
4On June 14, 2001, DNREC held a workshop to review draft protocols prepared by the U.S.
Fish and Wildlife Service for this project based on previous wetland assessment studies including
one for the Maryland portion of the Nanticoke watershed. Fourteen participants included
representatives from DNREC, Delaware Natural Heritage Program, Maryland Department of
Natural Resources, Maryland Department of the Environment, Smithsonian Environmental
Research Center, and U.S. Geological Survey (see Acknowledgments).
Functional assessment of wetlands can involve many parameters. Typically such assessments
have been done in the field on a case-by-case basis, considering observed features relative to
those required to perform certain functions or by actual measurement of performance. The
present study does not seek to replace the need for such evaluations as they are the ultimate
assessment of the functions for individual wetlands. Yet, for a watershed analysis, basin-wide
16
field-based assessments are not practical or cost-effective or even possible given access
considerations. For watershed planning purposes, a more generalized assessment is worthwhile
for targeting wetlands that may provide certain functions, especially for those functions
dependent on landscape position and vegetation life form. Subsequently, these results can be
field-verified when it comes to actually evaluating particular wetlands for acquisition purposes,
e.g., for conservation of biodiversity or for preserving flood storage capacity. Current aerial
photography may also be examined to aid in further evaluations (e.g., condition of
wetland/stream buffers or adjacent land use) that can supplement our preliminary assessment.
This study employs a watershed assessment approach that may be called "Watershed-based
Preliminary Assessment of Wetland Functions" (W-PAWF). W-PAWF applies general
knowledge about wetlands and their functions to develop a watershed overview that highlights
possible wetlands of significance in terms of performance of various functions. To accomplish
this objective, the relationships between wetlands and various functions must be simplified into a
set of practical criteria or observable characteristics. Such assessments could also be further
expanded to consider the condition of the associated waterbody and the neighboring upland or to
evaluate the opportunity a wetland has to perform a particular function or service to society, for
example.
W-PAWF usually does not account for the opportunity that a wetland has to provide a function
resulting from a certain land-use practice upstream or the presence of certain structures or land-uses
downstream. For example, two wetlands of equal size and like vegetation may be in the
right landscape position to retain sediments. One, however, may be downstream of a land-clearing
operation that has generated considerable suspended sediments in the water column,
while the other is downstream from an undisturbed forest. The former should be actively
performing sediment trapping in a major way, while the latter is not. Yet if land-clearing takes
place in the latter area, the second wetland will likely trap sediments as well as the first wetland.
The entire analysis typically tends to ignore opportunity since such opportunity may occurred in
the past or may occur in the future and the wetland is awaiting a call to perform this service at
higher levels than presently. An exception would be for a wetland type that would not normally
be considered significant for a particular function (e.g., sediment retention), but due to current
land use of adjacent areas now receives substantial sediment input and thereby performs the
function at a significant level.
W-PAWF also does not consider the condition of the adjacent upland (e.g., level of disturbance)
or the actual water quality of the associated waterbody which may be regarded as important
metrics for assessing the health of individual wetlands (not part of this study). Collection and
analysis of these data were done as another part of this study but were not incorporated into the
preliminary functional assessment.
We further emphasize that the preliminary assessment does not obviate the need for more
detailed assessments of the various functions. This assessment should be viewed as a starting
point for more rigorous assessments, as it attempts to cull out wetlands that may likely provide
significant functions based on generally accepted principles and the source information used for
17
this analysis. This type of assessment is most useful for regional or watershed planning
purposes. For site-specific evaluations, additional work will be required, especially field
verification and collection of site-specific data for potential functions (e.g., following the HGM
assessment approach as described by Brinson 1993a and other onsite evaluation procedures).
This is particularly true for assessments of fish and wildlife habitats and biodiversity. Other
sources of data may exist to help refine some of the findings of this report. Additional modeling
could be done, for example, to identify habitats of likely significance to individual species of
animals (based on their specific life history requirements).
Wetland Restoration Site Inventory
The results of this inventory were derived from air photointerpretation with review of hydric soils
data and updated wetland and land use/cover geospatial data. Time did not permit for field
checking, so results should be considered conservative. Areas identified as potential Type 1
restoration sites had visible evidence of restoration potential (e.g., wet depressions in cropland
and fill sites without buildings).
Type 2 sites could be expanded to include wetlands where the adjacent land use may produce
significant adverse impacts on the quality of the wetland, but this was not an objective of our
project. Many, if not most, wetlands in the watershed could be highlighted as having potentially
significant adverse impacts from adjacent land use practices as many wetlands are surrounded by
cropland. Many of these wetlands, however, were identified as being adversely impacted by
ditching. In addition, by examining the wetland buffer map, one can extract information on land
use practices contiguous with a wetland which could be used to ascertain potentially negative
impacts from external sources.
Rather than piecemeal restoration of small isolated wetlands, wetland restoration of large wetland
blocks (e.g., restoring huge flatwood interfluves) appears more beneficial to a goal of restoring
wetland ecosystems. To accomplish this, hydric soil information should be consulted. These
data will reveal significantly larger areas of hydric soils, presumably former wetlands that are
now cultivated where smaller presently isolated farmed wetlands, small impoundments, and/or
vegetated wetlands could be linked together to form a larger vegetated wetland that can be
connected to an existing wetland. Where hydric soil data are not available in digital form, this
could be done by visual examination of soil survey maps or perhaps by simply drawing lines
around the ditch network to predict the extent of former wetlands. This type of evaluation can be
made by consulting the wetland restoration site map which can be used as a reference for
identification large-scale restoration projects. Field work, however, is required to evaluate the
true restoration potential of any site as there are often limitations and other issues (e.g.,
landowner support) that can only be determined during field inspection.
Ditch Inventory
Photointerpretation of aerial photographs was performed to identify ditches in this watershed.
Although limited field work was performed for this project, such work did not focus on the
18
ditches. Additional work should be done in the future to verify the accuracy and completeness of
this inventory. Based on such work, some revision of the database may be required. In any
event, the existing data present a good perspective on the extent of ditching throughout the
watershed.
19
Appropriate Use of this Report
The report provides a basic characterization of wetlands in the Delaware portion of the Nanticoke
watershed including a preliminary assessment of wetland functions. Keeping in mind the
limitations mentioned above, the results are a first-cut or initial screening of the watershed's
wetlands to designate wetlands that may have a significant potential to perform different
functions. The targeted wetlands have been predicted to perform a given function at a significant
level presumably important to the watershed's ability to provide that function. "Significance" is a
relative term and is used in this analysis to identify wetlands that are likely to perform a given
function at a level above that of wetlands not designated. Review of these preliminary findings
and consideration of additional information not available to us may identify the need to modify
some of the criteria used to identify wetlands of potential significance for certain functions.
While the results are useful for gaining an overall perspective of the watershed's wetlands and
their relative importance in performing certain functions, the report does not identify differences
among wetlands of similar type and function. The latter information is often critical for making
decisions about wetland acquisition and designating certain wetlands as more important for
preservation versus others with the same categorization. Additional information may be gained
through consulting with agencies having specific expertise in a subject area and by conducting
field investigations to verify the preliminary assessments. When it comes to actually acquiring
wetlands for preservation, other factors must be considered. Such factors may include: 1) the
condition of the surrounding area, 2) the ownership of the surrounding area and the wetland
itself, 3) site-specific assessment of wetland characteristics and functions, 4) more detailed
comparison with similar wetlands based on field data, and 5) advice from other agencies (federal,
state, and local) with special expertise on priority resources (e.g., for wildlife habitat, contact
appropriate federal and state biologists). The latter agencies may have site-specific information
or field-based assessment methods that can aid in further narrowing the choices to help insure
that the best wetlands are acquired for the desired purpose.
The report is a watershed-based wetland characterization for the Nanticoke watershed. The
report does not make comparisons with other watersheds, although comparisons between
subbasins within this watershed were made from the “natural habitat integrity” standpoint. Be
advised that there may be characteristics (e.g., water quality and habitat concerns) that actually
make acquisition, restoration, or preservation of certain wetlands in one of these subbasins, a
higher priority than protection of similar wetlands in the other subbasins. This was beyond the
scope of the present study.
The report is useful for natural resource planning as an initial screening for considering
prioritization of wetlands (for acquisition, restoration, or strengthened protection), as an
educational tool (e.g., helping better our understanding of wetland functions and the relationships
between wetland characteristics and performance of individual functions), and for characterizing
the differences among wetlands (both form and function). It can also serve as benchmark for
documenting future trends in wetlands, river-stream corridors, and other natural features.
20
Rationale for Preliminary Functional Assessments
Nine functions were evaluated: 1) surface water detention, 2) streamflow maintenance, 3)
nutrient transformation, 4) sediment and other particulate retention, 5) shoreline stabilization, 6)
fish and shellfish habitat, 7) waterfowl and waterbird habitat, 8) other wildlife habitat, and 9)
biodiversity. The criteria used for identifying these functions using the digital wetland database
are discussed below. The criteria were developed by the senior author of the report and reviewed
and modified for the subject watersheds based on comments from an ad hoc group of wetland
specialists working on Delaware’s Nanticoke River watershed.
In developing a protocol for designating wetlands of potential significance, wetland size was
generally disregarded from the criteria, with few exceptions (i.e., other wildlife habitat and
biodiversity functions). This approach was followed because it was felt that the State and others
using the digital database and charged with setting priorities should make the decision on
appropriate size criteria as a means of limiting the number of priority wetlands, if necessary. Our
study was intended to present a more expansive characterization of wetlands and their likely
functions and not to develop a rapid assessment method for ranking wetlands for acquisition,
protection, or other purposes. The criteria for identifying different levels of potential
significance can be modified in the future based on review of this report’s findings and field
evaluation. Note that palustrine farmed wetlands have not been identified as being significant for
any function. They were viewed as severely degraded wetlands that perform various functions at
minimal levels. Consequently, they represented sites where substantial gains in wetland
functions may be achieved through restoration projects.
Surface Water Detention
This function is important for reducing downstream flooding and lowering flood heights, both of
which aid in minimizing property damage and personal injury from such events. In a landmark
study on the relationships between wetlands and flooding at the watershed scale, Novitzki (1979)
found that watersheds with 40 percent coverage by lakes and wetlands had significantly reduced
flood flows -- lowered by as much as 80 percent -- compared to similar watersheds with no or
few lakes and wetlands in Wisconsin. Floodplain wetlands, other lotic wetlands (basin and flat
types), estuarine fringe wetlands along coastal rivers, and estuarine island wetlands in these
rivers provide this function at significant levels. Wetlands dominated by trees and/or dense
stands of shrubs (with higher frictional resistance) could be deemed to provide a higher level of
this function as such vegetation may further aid in flood desynchronization versus similar
wetlands with emergent cover. Trees and dense shrubs produce high roughness which helps
dissipate energy and lower velocity of flood waters. Yet, this requirement was not applied to the
data set as emergent wetlands along waterways are also likely to provide significant flood
storage. Floodplain width could also be an important factor in evaluating the significance of
performance of this function by individual wetlands (e.g., for acquisition or strengthened
protection). There is no quantitative information for establishing a significance threshold based
on size, so floodplain width was not used as a selection factor in this study.
For this analysis, the following correlations were used:
21
High - Estuarine Fringe, Estuarine Island, Lotic Floodplain, Lotic Basin, Lotic Fringe,
Lentic Basin wetlands, and Throughflow Ponds (=in-stream)
Moderate - Terrene wetlands that are not ditched (no size criterion; excluding Slope
wetlands) amd Lotic Flat wetlands
Some - Other Ponds and Terrene ditched wetlands (excluding Slope wetlands)
Streamflow Maintenance
Many wetlands are sources of groundwater discharge and some may be in a position to sustain
streamflow in the watershed. Such wetlands are critically important for supporting aquatic life in
streams. Terrene headwater wetlands (by definition, the sources of streams) perform these
functions at notable levels. Lotic wetlands along first order streams may also be important for
streamflow maintenance, so they were also designated as headwater wetlands. Groundwater
discharging into streamside wetlands may contribute substantial quantities of water for sustaining
baseflows. Floodplain wetlands are known to store water in the form of bank storage, later
releasing this water to maintain baseflows. This also aids in reducing flood peaks and improving
water quality (Whiting 1998). Among several key factors affecting bank storage are porosity and
permeability of the bank material, the width of the floodplain, and the hydraulic gradient
(steepness of the water table). The wider the floodplain, the more bank storage given the same
soils. Gravel floodplains drain in days, sandy floodplains in a few weeks to a few years, silty
floodplains in years, and clayey floodplains in decades. In good water years, wide sandy
floodplains may help maintain baseflows.
For this analysis, the following correlations were used:
High - Terrene and Lotic headwater wetlands that are not ditched, Lentic headwater
wetlands, and Outflow Ponds and Lakes (classified as PUB... on NWI), and other
headwater Ponds
Moderate - Lotic Floodplain wetlands, Throughflow Ponds and Lakes (classified as
PUB... on NWI), and Lentic former floodplain wetlands
Some - Terrene and Lotic ditched headwater wetlands
Nutrient Transformation
All wetlands recycle nutrients, but those having a fluctuating water table are best able to recycle
nitrogen and other nutrients. Vegetation slows the flow of water which causes deposition of
mineral and organic particles and nutrients (nitrogen and phosphorus) bound to them, whereas
hydric soils are the places where chemical transformations occur (Carter 1996). Microbial action
in the soil is the driving force behind chemical transformations in wetlands. Microbes need a
22
food source -- organic matter -- to survive, so wetlands with high amounts of organic matter
should have an abundance of microflora to perform the nutrient cycling function. Wetlands are
so effective at filtering and transforming nutrients that artificial wetlands are constructed for
water quality renovation (Hammer 1992). Natural wetlands performing this function help
improve local water quality of streams and other watercourses.
Numerous studies have demonstrated the importance of wetlands in denitrification. Simmons et
al. (1992) found high nitrate removal (greater than 80%) from groundwater during both the
growing season and dormant season in Rhode Island streamside (lotic) wetlands. Groundwater
temperatures throughout the dormant season were between 6.5 and 8.0 degrees C, so microbial
activity was not limited by temperature. Even the nearby upland, especially transitional areas
with somewhat poorly drained soils, experienced an increase in nitrogen removal during the
dormant season. This was attributed to a seasonal rise in the water table that exposed the upper
portion of the groundwater to more organic matter (nearer the ground surface), thereby
supporting microbial activity and denitrification. Riparian forests dominated by wetlands have a
greater proportion of groundwater (with nitrate) moving within the biologically active zone of the
soil that makes nitrate susceptible to uptake by plants and microbes (Nelson et al. 1995).
Riparian forests on well-drained soils are much less effective at removing nitrate. In a Rhode
Island study, Nelson et al. (1995) found that November had the highest nitrate removal rate due
to the highest water tables in the poorly drained soils, while June experienced the lowest removal
rate when the deepest water table levels occurred. Similar results can be expected to occur in the
Nanticoke River watershed. For bottomland hardwood wetlands, DeLaune et al. (1996) reported
decreases in nitrate from 59-82 percent after 40 days of flooding wetland soil cores taken from
the Cache River floodplain in Arkansas. Moreover, they surmised that denitrification in these
soils appeared to be carbon-limited: increased denitrification took place in soils with greater
amounts of organic matter in the surface layer.
Nitrogen fixation is accomplished in wetlands by microbial-driven reduction processes that
convert nitrate to nitrogen gas. Nitrogen removal rates for freshwater wetlands are very high
(averaging from 20-80 grams/square meter) (Bowden 1987). The following information comes
from a review paper on this topic by Buresh et al. (1980). Nitrogen fixation has been attributed
to blue-green algae in the photic zone at the soil-water interface and to heterotrophic bacteria
associated with plant roots. In working with rice, Matsuguchi (1979) believed that the
significance of heterotrophic fixation in the soil layer beyond the roots has been underrated and
presented data showing that such zones were the most important sites for nitrogen fixation in a
Japanese rice field. This conclusion was further supported by Wada et al. (1978). Higher
fixation rates have been found in the rhizosphere of wetland plants than in dryland plants.
Phosphorus removal is largely done by plant uptake (Patrick, undated manuscript). Wetlands
that accumulate peat have a great capacity for phosphorus removal. Wetland drainage can,
therefore, change a wetland from a phosphorus sink to a phosphorus source. This is a significant
cause of water quality degradation in many areas of the world including the United States, where
wetlands are drained for agricultural production. Hydric soils with significant clay constituents
fix phosphorus due to its interaction with clay and inorganic colloids. Reduced soils have more
23
sorption sites than oxidized soils (Patrick and Khalid 1974), while the latter soils have stronger
bonding energy and adsorb phosphorus more tightly.
From the water quality standpoint, wetlands associated with watercourses are probably the most
noteworthy. Numerous studies have found that forested wetlands along rivers and streams
(“riparian forested wetlands”) are important for nutrient retention and sedimentation during
floods (Whigham et al. 1988; Yarbro et al. 1984; Simpson et al. 1983; Peterjohn and Correll
1982). This function by forested riparian wetlands is especially important in agricultural areas.
Brinson (1993b) suggests that riparian wetlands along low order streams may be more important
than those along higher order streams.
Wetlands with seasonally flooded and wetter water regimes (including tidal regimes - seasonally
flooded-tidal, irregularly flooded, and regularly flooded) were identified as having potential to
recycle nutrients at high levels of performance. Estuarine vegetated fringe and island wetlands
were similarly designated for like reasons. The soils of these wetlands should have substantial
amounts of organic matter that would promote microbial activity.
Wetlands with a temporarily flooded water regime including those in tidal environments
(temporarily flooded-tidal) were identified as having a moderate potential for performing this
function. Terrene outflow wetlands surrounded by cropland (50% or more of their upland
perimeter is in contact with cropland) were deemed to have some potential for nutrient
transformation. Since farming often introduces agrochemicals and sediment into streams,
wetlands between cropland and streams lie in landscape positions that favor recycling of
nutrients derived from runoff.
For this analysis, the following correlations were used:
High - All vegetated wetlands and mixed unconsolidated bottom-vegetated wetlands with
seasonally flooded (C), seasonally flooded/saturated (E), semipermanently flooded
(F), seasonally flooded-tidal (R), irregularly flooded (P), and regularly flooded (N)
water regimes (this includes Estuarine, Lotic, Terrene, and Lentic wetlands -
mostly floodplain, basin, interfluve-basin, and fringe types)
Moderate - Lotic flat and floodplain-flat wetlands with temporarily flooded (A) and
temporarily flooded-tidal (S) water regimes
Some - Terrene vegetated wetlands surrounded by >50% farmland
Retention of Sediments and Other Particulates
Many wetlands owe their existence to being located in areas of sediment deposition. This is
especially true for floodplain wetlands. This function supports water quality maintenance by
24
capturing sediments with bonded nutrients or heavy metals (as in and downstream of urban
areas). Estuarine and floodplain wetlands plus lotic and lentic fringe and basin wetlands
(including lotic ponds) are likely to trap and retain sediments and particulates at significant
levels. Lotic flat wetlands are flooded only for brief periods and less frequently than the
wetlands listed above due to their elevation. They were classified as having moderate potential
for sediment retention. For this analysis, lotic flats that were seasonally saturated were also
included in the moderate category, but further evaluation might justify changing their potential to
some since they are not inundated. Terrene outflow wetlands surrounded by cropland may now
perform this function at some level of potential significance due to erosion of tilled soils.
Isolated ponds may be locally significant in retaining such materials, and were also designated as
having possible some potential.
For this analysis, the following correlations were used:
High - Estuarine Fringe, Estuarine Island, Lentic Basin, Lentic Fringe, Lotic Floodplain,
Lotic Basin, Lotic Fringe and Throughflow Pond (in-stream)
Moderate - Lotic Flat, Terrene Basin, Terrene Fringe-pond, and Terrene Interfluve Basin
wetlands, Isolated Ponds, and Outflow Ponds
Some - Terrene Flat and Interfluve Flat wetlands surrounded by >50% cropland
Shoreline Stabilization
Vegetated wetlands along rivers and streams provide this function. Vegetation stabilizes the soil,
thereby preventing erosion. Wetlands adjacent to inland waters serve as buffers to reduce
erosion of uplands from flowing waters and thereby stabilize shorelines. For this analysis, the
following correlations were used:
High - Estuarine vegetated wetlands, Lotic wetlands (vegetated including tidal types;
except island wetlands), Lentic wetlands (vegetated, except island types), and
Terrene Fringe-pond wetlands
Provision of Fish and Shellfish Habitat
The assessment of potential habitat for fish and shellfish was based on generalities that could be
refined for particular species of interest by others at a later date. For tidal areas, the assessment
emphasized palustrine and riverine tidal emergent wetlands, unconsolidated shores (tidal flats)
and estuarine wetlands. For nontidal regions, palustrine aquatic beds5 and semipermanently
flooded wetlands ranked higher than seasonally flooded types due to the longer duration of
surface water. Palustrine forested wetlands along streams (lotic stream wetlands) were deemed
5No palustrine aquatic beds were mapped, but these areas could be important fish habitat.
25
important for maintaining fish and shellfish habitat since their canopies help moderate water
temperatures. Ponds and the shallow marsh-open water zone of impoundments were identified
as wetlands having some potential for fish and shellfish habitat.
Other wetlands providing significant fish habitat may exist, but were not be identified due to the
study methods. Such wetlands may be identified based on actual observations or culled out from
site-specific fisheries information that may be available from the State. Also recall that this
assessment is focused on wetlands, not deepwater habitats, hence the exclusion of the latter from
this analysis, despite widespread recognition that rivers, streams, ponds, and impoundments are
the primary residences of fish and shellfish. Moreover, all wetlands that are significant for the
streamflow maintenance function could be considered vital to sustaining the watershed's ability
to provide in-stream fish and shellfish habitat. While these wetlands may not be providing
significant fish and shellfish habitat themselves, they support base flows essential to keeping
water in streams for aquatic life.
For this analysis, the following correlations were used:
High - Estuarine Emergent, Estuarine Unconsolidated Shore, Palustrine Tidal Emergent
(including mixtures with Scrub-Shrub and Forested), Riverine Tidal
Unconsolidated Shore, Riverine Tidal Emergent, Palustrine Semipermanently
Flooded, Palustrine Aquatic Bed, Palustrine Unconsolidated Bottom/vegetated
wetland (Emergent, Scrub-Shrub, or Forested), Palustrine vegetated wetland with
a Permanently Flooded water regime, and Ponds associated with Semipermanently
Flooded vegetated wetlands
Moderate - Lotic Stream wetlands that are Palustrine Emergent (including mixtures with
Scrub-Shrub or Forested wetlands that are seasonally flooded/saturated), and
Throughflow Ponds
Some - Outflow Ponds and Isolated Ponds
Important for Stream Shading - Lotic Stream wetlands that are Palustrine Forested
wetlands (includes mixes where forested wetland predominates; excluding those
along intermittent streams)
Provision of Waterfowl and Waterbird Habitat
Wetlands considered to be important waterfowl and waterbird habitat were estuarine wetlands
(vegetated or not), riverine emergent wetlands, estuarine and riverine unconsolidated shores6
6The only estuarine or riverine unconsolidated shore mapped was a temporarily flooded-tidal
26
(excluding temporary flooded-tidal), palustrine tidal and riverine tidal emergent wetlands
(including emergent/shrub mixtures), semipermanently flooded wetlands, mixed open water-emergent
wetlands (palustrine and lacustrine), and aquatic beds. For this analysis, palustrine
tidal scrub-shrub/emergent wetlands and tidal forested/emergent wetlands were designated as
having moderate significance for these birds, yet they should be evaluated to determine if their
status should be upgraded to high potential. Ponds were considered to have some potential for
providing waterfowl and waterbird habitat.7
Wetlands that may be significant to wood duck were identified, since wooded streams are
particularly important for them. Seasonally flooded lotic wetlands that were forested or mixtures
of trees and shrubs (excluding those along intermittent streams) were deemed as wetlands with
significant potential for use by wood ducks. Wetlands listed as having high potential for
waterfowl and waterbird habitat also include some types important to wood ducks (e.g.,
semipermanently flooded lotic shrub/emergent wetlands).
Seasonally flooded emergent wetlands (including mixtures with shrubs) were not designated as
potentially significant for waterfowl and waterbirds. Field checking of these types may reveal
that some are freshwater marshes that may provide significant habitat. If so, these types may be
added to the wetlands of significance in the future. Other wetlands worthy of further
consideration are forested wetlands bordering estuarine wetlands. They may be important for
colonial nesting birds. If they provide such habitat in the Nanticoke watershed, then they should
be added to the list.
For this analysis, the following correlations were used:
High - Estuarine Emergent, Estuarine Unconsolidated Shore, Riverine Tidal Emergent,
Riverine Tidal Unconsolidated Shore (Regularly Flooded), Palustrine
Semipermanently Flooded, Palustrine Aquatic Bed, Palustrine Tidal Emergent,
Palustrine Tidal Emergent/Scrub-Shrub, Palustrine vegetated wetlands that are
Permanently Flooded, and Ponds associated with Semipermanently Flooded
riverine one.
7Ponds on wildlife management areas (e.g., refuges) should be considered to be of moderate
significance due to their management. Since we did not have the location of such refuges in our
digital database, these ponds could not be separated from the rest of the ponds. Hence, all ponds
were designated as having some potential for this function.
27
vegetated wetlands
Moderate - Palustrine Tidal Scrub-Shrub/Emergent and Forested/Emergent
Some - Other Palustrine Unconsolidated Bottom
Significant for Wood Ducks - Lotic wetlands (excluding those along intermittent streams)
that are Forested or Scrub-shrub wetlands or mixtures of these two types
(including freshwater tidal and nontidal), and Lotic wetlands that are
Forested/Emergent with a Seasonally Flooded/Saturated or wetter water regime
(including Seasonally Flooded-Tidal) and Unconsolidated Bottom/Forested
Provision of Other Wildlife Habitat
The provision of other wildlife habitat by wetlands was evaluated in general terms. Species-specific
habitat requirements were not considered. In developing an evaluation method for
wildlife habitat in the glaciated Northeast, Golet (1972) designated several types as outstanding
wildlife wetlands including: 1) wetlands with rare, restricted, endemic, or relict flora and/or
fauna, 2) wetlands with unusually high visual quality and infrequent occurrence, 3) wetlands with
flora and fauna at the limits of their range, 4) wetlands with several seral stages of hydrarch
succession, and 5) wetlands used by great numbers of migratory waterfowl, shorebirds, marsh
birds, and wading birds. Golet subscribed to the principle that in general, as wetland size
increases so does wildlife value, so wetland size was important factor for determining wildlife
habitat potential in his approach. Other important variables included dominant wetland class,
site type (bottomland v. upland; associated with waterbody v. isolated), surrounding habitat type
(e.g., natural vegetation v. developed land), degree of interspersion (water v. vegetation), wetland
juxtaposition (proximity to other wetlands), and water chemistry.
For this project, wetlands important to waterfowl and waterbirds were identified in a separate
assessment (see above). Emphasis for assessing "other wildlife" was placed on conditions that
would likely provide significant habitat for other vertebrate wildlife (mainly herps, interior forest
birds, and mammals). Opportunistic species that are highly adaptable to fragmented landscapes
were not among the target organisms, since there seems to be more than ample habitat for these
species now and in the future. Rather, animals whose populations may decline as wetland
habitats become fragmented by development are of more concern. For example, breeding
success of neotropical migrant birds in fragmented forests of Illinois was extremely low due to
high predation rates and brood parasitism by brown-headed cowbirds (Robinson 1990).
Newmark (1991) reported local extinctions of forest interior birds in Tanzania due to
fragmentation of tropical forests. Fragmentation of wetlands is an important issue for wildlife
managers to address. Some useful references on fragmentation relative to forest birds are Askins
et al. (1987), Robbins et al. (1989), Freemark and Merriam (1986), and Freemark and Collins
(1992). The latter study includes a list of area-sensitive or forest interior birds for the eastern
United States. The work of Robbins et al. (1989) is particularly relevant to the study watersheds
as they addressed area requirements of forest birds in the Mid-Atlantic states. They found that
28
species such as the black-throated blue warbler, cerulean warbler, Canada warbler, and black-and-
white warbler required very large tracts of forest for breeding. Table 2 lists some area-sensitive
birds for the region. Ground-nesters, such as veery, black-and-white warbler, worm-eating
warbler, ovenbird, waterthrushes, and Kentucky warbler, are particularly sensitive to
predation which may be increased in fragmented landscapes. Robbins et al. (1989) suggest a
minimum size of 7,410 acres to retain all species of the forest-breeding avifauna in the Mid-
Atlantic region.
The analysis identified two wetland types as potentially highly significant for other wildlife: 1)
large wetlands (> 20 acres) regardless of vegetative cover but excluding pine plantations, and 2)
smaller diverse wetlands (10-20 acres with multiple cover types). These two categories covered
most wetlands along stream corridors that connect large wetland complexes. Other vegetated
wetlands were designated as having some potential significance for providing wildlife habitat.
Given the general nature of this assessment of "other wildlife habitat," the State may want to
refine this assessment in the future by having biologists designate "target species" that may be
used to identify important wildlife habitats in the Nanticoke watershed. After doing this, they
could identify criteria that may be used to identify potentially significant habitat for these species
in the watershed. Dr. Hank Short (U.S. Fish and Wildlife Service, retired) compiled a matrix
listing 332 species of wildlife and their likely occurrence in wetlands of various types in New
England from ECOSEARCH models (Short et al. 1996) that he developed with Dr. Dick
DeGraaf (U.S. Forest Service) and Dr. Jay Hestbeck (U.S. Fish and Wildlife Service).8 DeGraaf
and Rudis (1986) summarized habitat, natural history, and distribution of New England wildlife.
Much of what is in the ECOSEARCH models comes from this source. These sources may be
useful starting points for determining relationships between wildlife and wetlands and may be
expanded to cover the Mid-Atlantic region.
For this analysis, the following correlations were used:
High - Large wetlands (>20 acres, excluding pine plantations) and small diverse wetlands
(10-20 acres with 2 or more covertypes),
Some - Other vegetated wetlands
8Copies of the matrix can be obtained by contacting R. Tiner (address on title page).
29
Table 2. List of some area-sensitive birds for forests of the Mid-Atlantic region. (Source:
Robbins et al. 1989).
Area (acres) at which
probability of occurrence
Species is reduced by 50%
Neotropical Migrants
Acadian flycatcher 37
Blue-gray gnatcatcher 37
Veery 49
Northern parula 1,280
Black-throated blue warbler 2,500
Cerulean warbler 1,700
Black-and-white warbler 543
Worm-eating warbler 370
Ovenbird 15
Northern waterthrush 494
Louisiana waterthrush 865
Canada warbler 988
Summer tanager 99
Scarlet tanager 30
Short-distance Migrants
Red-shouldered hawk 556
Permanent Residents
Hairy woodpecker 17
Pileated woodpecker 408
30
Conservation of Biodiversity
In the context of this report, the term "biodiversity" is used to identify certain wetland types that
appear to be scarce or relatively uncommon in the watershed, or individual wetlands that possess
several different covertypes (i.e., diverse wetland complexes), or complexes of large wetlands.
Schroeder (1996) noted that to conserve regional biodiversity, maintenance of large-area habitats
for forest interior birds is essential. As noted above, Robbins et al. (1989) suggest a minimum
forest size of 7,410 acres to retain all species of the forest-breeding avifauna in the Mid-Atlantic
region.
For recognizing the conservation of biodiversity function, we attempted to highlight areas that
may contribute to the preservation of an assemblage of wetlands that encompass the natural
diversity of wetlands in the Nanticoke watershed. Forested areas 7,410 acres and larger that
contained contiguous palustrine forested wetlands and upland forests were designated as
important for maintaining regional biodiversity of avifauna based on recommendations by
Robbins et al. (1989). We also identified a few other large wetlands in the watershed (e.g.,
possibly important for interior nesting birds and wide-ranging wildlife in general) and wetlands
that were uncommon types (based on mapping classification and not on Natural Heritage
Program data). All riverine tidal wetlands and oligohaline wetlands were identified as
significant for this function because they are often colonized by a diverse assemblage of plants
and are among the most diverse plant communities in the Mid-Atlantic region.
Use of Natural Heritage Program data and GAP data have been suggested, but these data were
not provided for the Nanticoke watershed in digital form for our use. Consequently, there was no
attempt to incorporate such data into our analysis. It is expected that Natural Heritage and GAP
information will be utilized at a later date by the State for more detailed planning and evaluation.
Consequently, the wetlands designated as potentially significant for biodiversity are simply a
foundation to build upon. Local knowledge of significant wetlands will further refine the list of
wetlands important for this function. For information on rare and endangered species, contact
the Delaware Natural Heritage Program.
For this analysis, the following correlations were used:
Wetlands with Atlantic white cedar or bald cypress, Estuarine oligohaline emergent
wetlands, Riverine tidal emergent wetlands, Palustrine tidal emergent wetlands (including
emergent and scrub-shrub mixtures), Palustrine emergent wetlands seasonally flooded
and wetter that are not ditched, diked, or excavated (including mixtures with scrub-shrub),
Palustrine tidal scrub-shrub wetlands, Semipermanently flooded Palustrine scrub-shrub
wetlands, Semipermanently flooded Palustrine forested wetlands (including
mixtures), Seasonally flooded and wetter Palustrine forested/emergent wetlands,
Palustrine tidal deciduous/evergreen forested wetlands, Palustrine tidal mixed
forested/scrub-shrub wetlands, Palustrine tidal evergreen forested wetlands, and
Palustrine wetlands within any 7,410-acre tract of contiguous forestland (both wetland
and upland forests)
31
Results
Wetland Classification and Inventory
Wetlands were classified according to the U.S. Fish and Wildlife Service's official wetland
classification system (Cowardin et al. 1979) and by landscape position, landform, and water flow
path descriptors following Tiner (2000). Summaries for the study area are given in Tables 3 and
4 and illustrated in Maps #1 through #4. The maps are presented on a compact disk which also
contains a copy of this report. Table 3 summarizes covertypes through the subclass level of the
Service’s classification ("NWI types"), while Table 4 tabulates statistical data on wetlands by
landscape position and landform ("HGM types"). Twenty-four percent of the watershed area
(which includes the river itself) is occupied by wetlands. If the river and its tributaries are
excluded from the watershed area, the percent of “land” represented by wetlands amounts to 25
percent.
Wetlands by NWI Types
According to the NWI, the Nanticoke watershed had 77,359 acres of wetlands, excluding linear
features (Table 3; Map #1). Nearly all of the wetlands were palustrine types, with only 80 acres
of estuarine wetlands and 34 acres of riverine wetlands. Seventy-nine percent of the wetlands
was forested (including mixed forested/scrub-shrub types). Many of the existing palustrine
scrub-shrub and scrub-shrub/emergent wetlands represent successional plant communities of cut-over
forested wetlands in various stages of regrowth. Ninety-eight percent of the wetlands was
nontidal (beyond tidal influence), while only two percent was tidal. About 71 percent of the
watershed’s wetlands was impacted by ditching, farming, impoundment, or excavation, with 65
percent alone being partly drained due to ditching and channelization. Four percent of the
wetlands was farmed. Only 419 wetland acres were impounded, while 666 acres were excavated.
Most (82%) of the watershed’s wetlands were seasonally saturated with high water tables in
winter and early spring (Table 4). Ten percent was seasonally flooded types. Only 2 percent of
the Nanticoke watershed’s wetlands was tidal. (Note: Palustrine farmed wetlands were not
included in the above statistics, since no water regime was attributed to them.)
The watershed also had 2,382 acres of deepwater habitats: 1,222 acres of tidal rivers, 138 acres
of nontidal rivers, 328 acres of estuarine river, and 693 acres of impounded lakes. In addition,
the watershed contained 532 miles of linear nontidal streams.
32
Table 3. Wetlands in the Nanticoke watershed classified by NWI wetland type to the class level
(Cowardin et al. 1979). Other modifiers have been deleted from NWI types for this compilation.
NWI Wetland Type Acreage
Estuarine Wetlands
Emergent (Oligohaline) 79.9
----------------------------- --------
Subtotal 79.9
Palustrine Wetlands
Emergent (Nontidal) 1,040.0
Emergent (Tidal) 87.5
Farmed 3,309.6
Scrub-Shrub/Emergent 4,210.9 (including 59.8 tidal)
Broad-leaved Deciduous Forested (Nontidal) 25,154.1 (including 267.7 cypress)
Broad-leaved Deciduous Forested (Tidal) 1,083.2
Needle-leaved Evergreen Forested 4,673.9 (including 12.6 tidal)
Mixed Forested (Nontidal) 17,622.6
Mixed Forested (Tidal) 182.5
Deciduous Forested/Emergent 320.0 (including 0.9 tidal)
Forested/Scrub-Shrub and Forested/Scrub-Shrub 12,343.1 (including 11.7 tidal;
25.5 cypress)
Deciduous Scrub-Shrub 1,496.5 (including 41.0 tidal)
Needle-leaved Evergreen Scrub-Shrub (Nontidal) 3,010.1
Scrub-Shrub (Nontidal) 2,047.9
Unconsolidated Bottom/Vegetated 40.4 (including 34.8 cypress)
Unconsolidated Bottom (Nontidal) 622.9 (including 7.9 uncon. shore)
----------------------------------------------------------- ------------------------------------------
Subtotal 77,245.2
Riverine Wetlands
Emergent (Tidal) 33.5
Unconsolidated Shore (Tidal) 0.3
-------------------------------------- -------------
Subtotal 33.8
GRAND TOTAL (ALL WETLANDS) 77,358.9
33
Table 4. Distribution of Nanticoke wetlands according to water regime.
Water Regime Percent of
Watershed’s Wetlands*
Temporarily Flooded 3.7
Saturated (Seasonally) 82.4
Seasonally Flooded 5.5
Seasonally Flooded/Saturated 4.9
Semipermanently Flooded 0.5
Permanently Flooded 0.7
Artificially Flooded 0.1
Regularly Flooded (tidal) 0.1
Irregularly Flooded (tidal) 0.1
Seasonally Flooded-Tidal 1.9
Temporarily Flooded-Tidal 0.1
*Excludes palustrine farmed wetlands.
34
Hydrogeomorphic-Type Wetlands9
A total of 3,947 wetlands (excluding ponds) was inventoried in the Nanticoke River watershed
and classified by their hydrogeomorphic features (Table 5; Maps #2-#4). Nearly 83 percent of
the individual wetlands (excluding ponds) occurred in terrene landscape positions (Map #2).
These wetlands accounted for 85 percent of the watershed’s wetland acreage. Lotic wetlands
were second-ranked in extent, making up 14 percent of the acreage and 16 percent of the number.
The remaining 1 percent of the acreage was comprised of estuarine wetlands (0.7% of the
acreage) lying along estuarine waters and lentic wetlands (0.3% of the acreage) associated lake
basins including large impoundments.
From the landform standpoint, interfluve wetlands accounted for 74 percent of the wetland
acreage (excluding ponds) (Map #3). Floodplain wetlands were next in abundance representing
13 percent of the acreage, while flats and basins comprised 7 percent and 5 percent, respectively.
Outflow wetlands were the predominant water flow path type (Map #4). They totaled nearly
62,000 acres and represented 81 percent of the wetland acreage. Throughflow wetlands ranked
next at 14 percent (10,532 acres), followed by isolated wetlands (3%; 2,678 acres) and
bidirectional flow wetlands (2%; 1,597 acres). Ponds were nearly equally divided between
outflow types (43%) and isolated types (39%), with the rest being throughflow types (18%).
Wetlands fragmented by major roads amounted to 4,411 acres. This represents about 6 percent
of the wetland acreage. If fragmentation was considered from the landscape perspective, the
figure would be much higher as many remnants of once larger wetland complexes (i.e.,
interfluves) are now surrounded by cropland. Also many minor roads cris-cross wetlands
throughout the watershed.
9All wetlands, except palustrine unconsolidated bottoms and shores, were characterized
by HGM-type descriptors. These exceptions were classified as pond or lake types and are
not reflected in the summary statistics.
35
Table 5. Wetlands (excluding ponds) in the Nanticoke watershed classified by landscape
position, landform, and water flow path (Tiner 2000). See Appendix for definitions.
Landscape Landform Water Flow # of Wetlands Acreage
Position
Estuarine 11 513.7
Fringe* Bidirectional 11 513.7
Lentic 50 252.3
Basin Bidirectional 3 5.8
Throughflow 21 94.3
Flat Throughflow 9 23.7
Fringe Throughflow 14 123.5
Island Throughflow 3 5.0
Lotic River 174 944.8
Floodplain Bidirectional** 117 812.3
Throughflow 6 28.0
Fringe Bidirectional** 50 104.2
Island Bidirectional** 1 0.3
Lotic Stream 443 9,708.6
Perennial 400 9,532.1
Basin Throughflow 25 66.5
Flat Throughflow 55 562.6
Floodplain Throughflow 298 8,745.5
Fringe Throughflow 22 157.5
Intermittent 4 15.6
Basin Throughflow 2 11.8
Flat Throughflow 2 3.8
36
Tidal 39 160.9
Floodplain Bidirectional 26 139.8
Fringe Bidirectional 13 21.1
Terrene 3269 65,328.3
Basin Isolated 820 956.5
Outflow 682 2,629.9
Throughflow 36 61.3
Flat Isolated 294 996.7
Outflow 289 3,321.4
Throughflow 53 303.7
Fringe Outflow 1 0.9
Interfluve Isolated 56 724.6
Outflow 1010 55,988.7
Throughflow 28 344.6
*Includes tidal freshwater wetlands contiguous with estuarine wetlands and along estuarine waters
**Freshwater tidal reach
37
Maps
Twenty-two maps were produced at 1:90,000 to profile the Nanticoke’s wetlands and watershed.
These maps have been distributed to the Delaware Department of Natural Resources and
Environmental Control. They are also included in a separate folder on the CD containing this
report. The report and accompanying maps may be put up on the NWI homepage
(wetlands.fws.gov) under “reports and publications” in the near future.
A list of the 22 maps follows:
Map 1 - Wetlands and Deepwater Habitats Classified by NWI Types
Map 2 - Wetlands Classified by Landscape Position
Map 3 - Wetlands Classified by Landform
Map 4 - Wetlands Classified by Water Flow Path
Map 5 - Potential Wetlands of Significance for Surface Water Detention
Map 6 - Potential Wetlands of Significance for Streamflow Maintenance
Map 7 - Potential Wetlands of Significance for Nutrient Transformation
Map 8 - Potential Wetlands of Significance for Sediment and Other Particulate Retention
Map 9 - Potential Wetlands of Significance for Shoreline Stabilization
Map 10 - Potential Wetlands of Significance for Fish and Shellfish Habitat
Map 11 - Potential Wetlands of Significance for Waterfowl and Waterbird Habitat
Map 12 - Potential Wetlands of Significance for Other Wildlife Habitat
Map 13 - Potential Wetlands of Significance for Biodiversity
Map 14 - Potential Wetland Restoration Sites
Map 15 - Extent of Ditching
Map 16 - Condition of Perennial River and Stream Corridors (200m)
Map 17 - Condition of Wetland Buffers (100m)
Map 18 - Condition of Pond and Lake Buffers (100m)
Map 19 - Extent of Natural Vegetation in the Watershed
Map 20 - Condition of Streams (Channelized or Dammed vs. Natural)
Map 21 - Condition of Vegetated Wetlands (Partly Drained/Excavated/Impounded vs. Not
Altered)
Map 22 - Potential Sites for Restoring Wildlife Travel Corridors
The first four maps depict wetlands by the Service’s classification system (NWI types) and by
landscape position, landform, and water flow path. Maps 5-13 highlight wetlands that may
perform each of the referenced functions at a significant level. Maps 14-22 address some other
important natural resource features of the watershed.
Summary of Preliminary Functional Assessment Data
38
The rationale for preliminary assessment of wetlands for performing each of nine functions and
designated wetland types of potential significance are given in the Methods section. Table 6
summarizes the results for each function for the watershed (see Maps 5-13), while the findings
for each subbasin are given in Appendix B.
Nearly 96 percent of the wetland acreage was identified as potentially significant for surface
water detention, while almost 91 percent was deemed as potentially significant for streamflow
maintenance. The headwater position of this portion of the Nanticoke watershed led to most
wetlands being designated as important for the latter function. For nutrient transformation, about
65 percent of the wetland acreage may have at least some potential, and a nearly equal amount
(67%) was identified as potentially significant for sediment and other particulate retention.
Approximately 15 percent of the wetland acreage may have potential for shoreline stabilization.
About 14 percent of the wetlands was predicted to have at least some potential as habitat for or
provide significant benefits to fish and shellfish. Please note that wetlands designated as
significant for the streamflow maintenance should also be considered vital to sustaining the
watershed's ability to provide in-stream fish habitat. Fifteen percent of the wetland acreage may
have some potential for providing waterfowl and waterbird habitat, with most of the designated
wetlands potentially benefitting wood duck. Almost 84 percent of the wetlands were identified
as potentially important as habitat for other wildlife. Wetlands listed as potentially important for
biodiversity represented about 39 percent of the wetland acreage. For this function, one large
contiguous forest of 21,069 acres contained 12,777 acres of wetland (85% of which was forested
or mixed forested/scrub-shrub types), while six large wetland complexes of the following sizes
were identified: 1,342 acres, 1,554 acres, 1,545 acres, 986 acres, 1,428 acres, and 4,458 acres.
These complexes plus the wetlands in the large contiguous forest accounted for 31 percent of the
watershed’s wetlands, while rare or uncommon wetland types comprised only 8 percent.
Readers should keep in mind that this assessment was based on remote sensing techniques and
specific studies that may have been published on various functions were not reviewed. In
particular, known sites important to maintaining biodiversity such as those on record with the
Delaware Natural Heritage Program were not consulted. Consequently, the listing is
conservative and represents a starting point, not an end point for an assessment of wetlands
important for various functions. These sources could be reviewed by the State at a later date to
add or delete wetlands from the list in their future planning and evaluation efforts.
39
Table 6. Preliminary functional assessment results for wetlands of the Nanticoke watershed.
% of Wetland
Function Potential Significance Acreage Acreage
Surface Water Detention High Potential 10,803 14.0
Moderate Potential 15,770 20.4
Some Potential 47,328 61.2
Streamflow Maintenance High Potential 15,772 20.4
Moderate Potential 7,520 9.7
Some Potential 46,915 60.6
Nutrient Transformation High Potential 9,625 12.4
Moderate Potential 2,020 2.6
Some Potential 38,832 50.2
Retention of Sediments
and Inorganic Particulates High Potential 10,931 14.1
Moderate Potential 2,681 3.5
Some Potential 38,358 49.6
Shoreline Stabilization High Potential 11,364 14.7
Fish/Shellfish Habitat High Potential 666 0.9
Moderate Potential 57 0.1
Some Potential 513 0.7
Shading Potential* 9,239 11.9
Waterfowl/Waterbird Habitat High Potential 644 0.8
Moderate Potential 55 0.1
Some Potential 596 0.8
Wood Duck Potential 10,279 13.3
Other Wildlife Habitat High Potential 60,670 78.4
Some Potential 3,945 5.1
Biodiversity Wetlands with Atlantic White Cedar 120 0.2
Wetlands with Bald Cypress 328 0.4
Estuarine Oligohaline Wetlands 80 1.0
Riverine Tidal Wetlands 34 -
Uncommon Fresh Tidal Wetlands 212 2.7
Uncommon Nontidal Wetlands 264 3.4
Wetter Palustrine Emergent Wetlands 95 0.1
Wetlands within 7,410+ acre Forest 12,777 16.5
Large Wetland Complexes (six: 1327 a;
1554; 1545; 986; 1428; 4458 a) 11,297 14.6
Potential Wetland Restoration Sites
40
Due to the history of human activities in this watershed, there are many opportunities for wetland
restoration. Over 55,000 acres of potential wetland restoration sites were identified (Map 14). A
total of 4,178 acres of Type 1 wetland restoration sites were identified in the Nanticoke
watershed and 50,909 acres of Type 2 sites (Table 7). Two-thirds of the watershed’s wetlands
were designated as Type 2 sites (degraded wetlands whose functions may be improved by various
types of restoration). Farmed wetlands (constituting 4 percent of the watershed’s wetlands) were
identified as potential Type 1 restoration sites, since their current wetland functions are minimal
due to severe modification. They represented 79 percent of the Type 1 restoration acreage.
The extent of ditching in this watershed is significant (see following subsection). As a result,
almost 99 percent of the Type 2 potential restoration sites consisted of partly drained (ditched)
wetlands. The effect of drainage on these wetlands must be evaluated in the field on a case-by-case
basis. Some of these wetlands may have minimal adverse effects, while many others may be
seriously impacted by the drainage ditches. For example, ditched wetlands with a seasonally
flooded/saturated water regime (e.g., PFO1Ed) may be less adversely impacted than those
classified with a temporarily flooded water regime (e.g., PFO1Ad). The extent of ditching has
been highlighted for potential restoration sites on the wetland restoration site map (Map 14) to
provide some visual perspective on the magnitude of ditching in the affected wetlands.
Some of the impounded wetlands listed under Type 2 sites may include both former vegetated
wetlands and uplands, whereas some of the impoundments designated as potential Type 1
restoration sites include former stream or river channels. Field investigations or an examination
of historical aerial photographs are required to sort out the differences. Nonetheless, most of the
latter types occupied landscape positions (i.e., adjacent to floodplains) where they could be
restored to provide floodplain wetland functions, if desirable.
Narrow man-made levees along channelized streams also represent potential Type 1 wetland
restoration sites, but were not included in the above statistics. Construction of many of these
levees involved depositing spoil material produced from stream channelization projects onto
wetlands. Complete removal of this fill would produce some gains in wetland acreage and
restore wetland hydrology to some degree. At a minimum, the hydrology of the affected
wetlands could be improved by creating openings in the levees in a sufficient number of places to
reconnect these landward wetlands with their adjacent streams. Clearly, this would improve the
surface water detention function of these wetlands.
41
Table 7. Acreage and number of potential wetland restoration sites in the Nanticoke watershed.
Potential Type 1 Restorations No. of Sites* Acreage
Effectively drained or filled former wetlands
(now dryland)** 57 84.5
Farmed wetlands 1,397 3,309.6
Impoundments (former vegetated
wetlands)*** 10 653.3
Excavated former vegetated wetlands 7 130.5
-------------------------------------------- ----------- -------------------
Total 1,471 4,177.9
Potential Type 2 Restorations No. of Sites* Acreage
Impounded Wetlands and Ponds
(formerly vegetated wetlands) 98 418.7
Ditched Palustrine Wetlands 2,886 50,155.7
Excavated Wetlands 371 334.2
------------------------------------- ----------- ------------
Total 3,355 50,908.6
*Sites relate to mapped polygons; one large wetland complex therefore may contain a
number of sites.
**Does not include narrow man-made levees along channelized streams.
***Includes undetermined acreage of former riverbed or streambed.
42
Extent of Ditching
A total of 1,128 miles of ditches was inventoried by this project. This figure amounts to 2.3
miles of ditches per square mile of land area. Map 15 shows the extent of ditching in the
Nanticoke watershed. Also note that besides the ditches, the watershed had 438 miles of
channelized nontidal rivers and streams, representing 80 percent of the total nontidal perennial
river and stream length in the watershed. The channelized stream segments can be interpreted as
opportunities for stream restoration. Priorities for such restoration might start with channelized
perennial and seasonally flooded/saturated intermittent streams.
Water Resource Buffer Analysis
Buffers were established around several water resource features to evaluate the condition of lands
immediately surrounding wetlands and waterbodies. The buffer excludes open water areas. .
Maps 16 through 18 show the condition of the 100m buffer around the following features: 1)
perennial rivers and streams (nontidal), 2) vegetated wetlands, and 3) ponds and lakes,
respectively. While the 100m buffer often includes some open water, our analysis focused on the
“land” portion of the buffer since this is the zone that may be vegetated or developed.
Approximately 59 percent of 100m buffer around perennial rivers and streams10 still possessed
natural vegetation intact, while 80 percent of the “developed” buffer consisted agricultural land.
Only 36 percent of the 100m buffer around vegetated wetland remains vegetated, while slightly
more (39%) of the buffer around ponds and lakes is vegetated.
Analyses were performed for buffers around various combinations of waterbodies, with the
following results: 1) perennial nontidal and tidal rivers and streams: 59 percent vegetated, 2)
perennial and intermittent nontidal rivers and streams and ditches: 41 percent vegetated, 3)
perennial and intermittent rivers and streams, tidal rivers, and ditches: 42 percent vegetated, and
4) perennial streams only (including intermittents with prolonged flows: R4SBEx, and excluding
impounded stream segments): 59 percent.
Readers should note that buffer areas mapped as agricultural land may represent opportunities to
restore natural vegetation along streams, wetlands, and other waterbodies. Such areas should
10Perennial streams include streams designated as seasonally flooded/saturated intermittent
streams (i.e., R4SBEx) which flow for long periods during the year, but not year-round. Such
streams were identified on the source data (U.S.Geological Survey DLGs) as perennial, but based
on our field experiences and those of Amy Jacobs (DNREC), they were determined to be
intermittent.
43
typically be cropland that may be readily revegetated with native woody species to restore
effectiveness of natural buffers.
Natural Habitat Integrity Indices
These indices were calculated for the entire Delaware portion of the watershed and for each
corresponding subbasin. Note stream corridor and various buffer analyses focus on the “land”
portion of the buffer (i.e., the area that may contain self-supporting vegetation) and excludes any
open water areas in that zone.
Values for the Entire Watershed
The values for the nine indices for the Delaware portion of the Nanticoke River watershed are
calculated and presented below.
Natural Cover Index = 128,028 acres of natural vegetation/312,779 acres of land in
watershed = 0.41
River-Stream Corridor Integrity Index for Perennials Only (100m buffer = 200m corridor)
= 28,092 acres of natural vegetation in buffer/47,302 acres of buffer = 0.59
Vegetated Wetland Buffer Index (100m) = 28,779 acres of natural vegetation in upland
buffer/79,380 acres of upland buffer = 0.36
Pond and Lake Buffer Index (100m) = 2,460 acres of natural vegetation in upland
buffer/6,289 acres of upland buffer = 0.39
Wetland Extent Index = 59,529 acres of wetlands/143,945 acres of hydric soil map units
= 0.41 (Note: Estimated from hydric soil data available for 85 percent of the watershed)
Standing Waterbody Extent Index = 1.0 due to impoundment and pond construction
Dammed Stream Flowage Index = 17.6 miles dammed/574.3 miles of perennial nontidal
rivers and streams = 0.03
Channelized Stream Length Index = 437.8 miles of channelized streams/556.7 miles of
perennial nontidal rivers and streams = 0.79
Wetland Disturbance Index = 54,550 acres of altered wetlands/77,362 acres of wetlands =
0.71
44
Composite Natural Habitat Integrity Index = ICNHI 100 = (0.5 x INC) + (0.125 x IRSCI200) +
(0.125 x IWB100) + (0.05 x IPLB100)+ (0.1 x IWE), + (0.1 x ISWE) - (0.1 x IDSF) - (0.1 x ICSL) - (0.1 x
IWD) = (0.5 x 0.41) + (0.125 x 0.59) + (0.125 x 0.36) + (0.05 x 0.39) + (0.1 x 0.41) + (0.1
x 1.0) - (0.1 x 0.03) - (0.1 x 0.79) - (0.1 x 0.71) = 0.485 - 0.153 = 0.33
The above indices provide evidence of a severely stressed system. A pristine watershed has an
index value of 1.0 for natural habitat integrity. The value of 0.33 for the Nanticoke watershed
indicates significant human modification. While stream corridors seem to be in somewhat
reasonable shape regarding natural vegetation (59% of the 200m corridor is in natural
vegetation), nearly two-thirds of the vegetated wetland buffer and 61 percent of the pond and
lake buffers have been developed. Overall, the Nanticoke watershed has lost 59 percent of both
its natural habitat and its original wetlands, while 79 percent of its streams have been
channelized, and 71 percent of its current wetlands are altered by ditches, diking, excavation, or
farming. Forty-one percent of the land in the watershed is covered with “natural vegetation,” 50
percent is in agriculture, and 9 percent is developed. If the response of this watershed to farming
and development is similar to that of Wisconsin watersheds studied by Wang et al. (1997), we
can expect significant degradation of water quality, since they found that watersheds with more
than half of their acreage in agriculture experienced significant declines in instream habitat
quality versus watersheds with less agriculture and more forest.
Summaries for Each Subbasin
A summary of vital statistics for each subbasin are presented in Tables 8 through 15, with results
of the preliminary assessment of wetland functions for each subbasin presented in Appendix B.
Wetland characteristics are outlined in Table 8. Land use and land cover features are presented
in Table 9. The condition of various stream buffers is presented in Table 10, while the condition
of the 100m buffer around lakes and ponds, and around wetlands are given in Tables 11 and 12,
respectively. Alterations of streams and the extent of ditching is tabulated in Table 13. Wetland
alterations are outlined in Table 14. Remotely-sensed natural habitat integrity indices are
summarized in Table 15. Application of the natural habitat integrity indices to individual
subbasins within the watershed could aid in targeting areas for preservation and restoration.
From the indices for the entire watershed, we have seen that this watershed is extremely impacted
by human activities, mainly agriculture. Gravelly Branch, with composite index value of 0.51,
appears to be in noticeably better condition than the other subbasins. All other subbasins have
composite index scores less than 0.40. Marshyhope Creek and Nanticoke River subbasins appear
to be in the worst condition, with composite index values of less than 0.30.
45
Table 8. Wetland acreage for each subbasin of the Nanticoke watershed by NWI type. Coding:
E2EM = Estuarine Emergent; PEM/SS-M = Palustrine Mixed Emergent and Scrub-Shrub; PEM =
Palustrine Emergent; Pf = Palustrine Farmed; PFO-M = Palustrine Mixed Forested; PFO/EM-M =
Palustrine Mixed Forested/Emergent; PFO/SS-M = Palustrine Mixed Forested/Scrub-Shrub; PFO-D =
Palustrine Deciduous Forested; PFO-E = Palustrine Evergreen Forested; PSS-M = Palustrine Mixed Scrub-
Shrub; PSS-D = Palustrine Deciduous Scrub-Shrub; PSS-E = Palustrine Evergreen Scrub-Shrub; PUB/V =
Palustrine Unconsolidated Bottom Mixed with Vegetated Wetland; PUB = Palustrine Unconsolidated
Bottom (includes Unconsolidated Shore); R1EM = Riverine Tidal Emergent Wetland
Broad Deep Gravelly Gum Marshyhope Nanticoke
Wetland Type Creek Creek Branch Branch Creek River
E2EM 33.1 - - - - 47.0
PEM/SS-M 1062.1 421.6 710.1 335.1 822.6 862.6
PEM 187.8 154.8 167.1 3.7 318.6 294.8
Pf 701.2 538.0 172.6 38.8 950.9 908.1
PFO/SS-M 3,917.7 1,228.7 933.3 1,875.3 4,034.6 2,862.0
PFO/EM-M 105.3 - - 7.3 201.1 6.4
PFO-M 1,409.2 3,363.3 3,326.1 1,400.8 2,725.6 3,071.7
PFO-D 4,584.3 3,455.8 1,641.5 1,085.9 9,316.5 6,153.1
PFO-E 1,141.8 1,270.8 1,133.2 105.1 548.1 474.9
PSS-M 749.1 357.6 502.6 182.5 153.1 103.1
PSS-D 534.8 175.6 71.4 137.7 320.5 256.5
PSS-E 952.9 787.7 440.1 272.3 363.6 193.5
PUB/V 41.3 - - - - -
PUB 218.9 106.3 15.4 30.6 36.7 215.0
R1EM 1.8 7.3 - - - 24.4
------------- ---------- ---------- --------- --------- ----------- ----------
Total 15,641.3 11,867.5 9,113.4 5,475.1 19,791.9 15,473.1
46
Table 9. Summary statistics for land use and landcover in subbasins of the Nanticoke watershed.
Acreage of Land Use/Cover Type (percent of total subbasin)
“Natural
Subbasin Developed Agriculture Vegetation”* Water
Broad Creek 6,920 (9%) 38,261 (51%) 29,650 (39%) 976 (1%)
Deep Creek 3,753 (9%) 15,655 (39%) 20,815 (51%) 364 (1%)
Gravelly Branch 1,499 (6%) 7,544 (31%) 15,321 (63%) 142 (<1%)
Gum Branch 1,042 (5%) 9,277 (48%) 8,967 (46%) 45 (<1%)
Marshyhope Creek 2,513 (4%) 33,988 (54%) 25,743 (41%) 124 (<1%)
Nanticoke River 11,480 (12%) 52,820 (57%) 27,533 (30%) 1394 (1%)
*Includes pine plantations and other commercial forests
47
Table 10. Condition of the 100m buffer along streams in each subbasin for four cases: 1)
perennial rivers and streams only (excluding tidal reach), 2) perennials and tidal, 3) perennials,
intermittents, and ditches, 4) perennials including tidal, plus intermittents and ditches, and 5)
perennial streams only (linears including R4SBEx). Buffer data addresses the “land” portion of
the buffer and does not include open water areas.
Percent of Buffer in “Natural Vegetation”
Subbasin Case 1 Case 2 Case 3 Case 4 Case 5
Broad Creek 58% 59% 42% 43% 59%
Deep Creek 65% 64% 48% 48% 65%
Gravelly Branch 80% 80% 61% 61% 81%
Gum Branch 73% 73% 49% 49% 73%
Marshyhope Creek 54% 54% 37% 37% 54%
Nanticoke River 51% 53% 32% 34% 50%
48
Table 11. Condition of the 100m buffer along lakes and ponds for each subbasin.
Subbasin Percent of Buffer in
“Natural Vegetation”
Broad Creek 42%
Deep Creek 41%
Gravelly Branch 57%
Gum Branch 44%
Marshyhope Creek 37%
Nanticoke River 34%
49
Table 12. Condition of the 100m buffer around vegetated wetlands for each subbasin.
Subbasin Percent of Buffer in
“Natural Vegetation”
Broad Creek 40%
Deep Creek 41%
Gravelly Branch 49%
Gum Branch 46%
Marshyhope Creek 28%
Nanticoke River 31%
50
Table 13. Disturbance values for streams and extent of ditching in each subbasin of the
Nanticoke River watershed. Note that totals do not always add up due to computer round-off
procedures.
Miles of Miles of Miles of
Channelized Flowing Dammed Miles of
Stream Perennial Stream Perennial Miles of
Subbasin (% of total)* Streams* (% of total)** Streams** Ditches
Broad Creek 77.3 (59%) 131.1 8.0 (6%) 138.7 251.8
Deep Creek 70.1 (87%) 80.2 3.1 (4%) 82.3 143.9
Gravelly Branch 37.2 (89%) 41.9 3.3 (7%) 45.0 77.0
Gum Branch 35.0 (96%) 36.3 - 36.3 55.2
Marshyhope Creek 110.3 (94%) 117.4 - 117.4 326.8
Nanticoke River 107.6 (75%) 143.1 3.1 (2%) 146.2 272.9
*Excludes tidal reach, impounded segments, and intermittent streams
**Excludes tidal reach and intermittent streams
51
Table 14. Extent of altered wetlands in each subbasin.
Ditched Farmed Impounded Excavated Total
Subbasin Acres Acres Acres Acres Acres
(% of
wetlands)
Broad Creek 8,695 701 199 239 9,834 (63%)
Deep Creek 7,909 538 117 103 8,667 (73%)
Gravelly Branch 4,827 173 61 25 5,086 (56%)
Gum Branch 4,353 39 7 28 4,427 (81%)
Marshyhope Creek 16,168 951 1 38 17,158 (87%)
Nanticoke River 8,203 908 34 232 9,377 (61%)
52
Table 15. Remotely-sensed natural habitat indices for each subbasin in the Delaware portion of
the Nanticoke River watershed. (Note: The River-Stream Corridor Index includes the tidal
reach.)
Remotely-sensed Natural Habitat Indices
Subbasin INC IRSCI200 IWB100 IPLB100 IWE ISWE IDSF ICSL IWD ICNHI
100
Broad Creek 0.40 0.59 0.40 0.42 0.45 1.0 0.06 0.59 0.63 0.36
Deep Creek 0.52 0.64 0.41 0.41 0.43 1.0 0.04 0.87 0.73 0.39
Gravelly Branch 0.63 0.80 0.49 0.57 0.52 1.0 0.07 0.89 0.56 0.51
Gum Branch 0.46 0.73 0.46 0.44 0.35 1.0 0.00 0.96 0.81 0.34
Marshyhope Creek 0.41 0.54 0.28 0.37 0.38* 1.0 0.00 0.94 0.87 0.28
Nanticoke River 0.30 0.53 0.31 0.34 0.36* 1.0 0.02 0.75 0.61 0.27
*Calculations based on part of subbasin where digital soils data were available (37% of
Marshyhope Creek subbasin and 92% of the Nanticoke River subbasin).
53
Wildlife Travel Corridors
Many wetlands and other natural habitats in the Nanticoke River watershed have become
fragmented by human actions. In particular, agricultural conversion of wetlands and neighboring
forests and channelization projects have divided many of these habitats into smaller parcels,
thereby reducing the connectivity among natural habitats. As one aid to help guide wildlife
habitat improvement in the watershed, a map showing some possible places for restoring
connectivity was compiled. Map 22 shows potential sites for restoring connectivity among
wildlife habitats through reforestation of 200m swaths. The designated lands should be open
land (mostly cropland) that are suitable for reforestation (with landowner permission).
Please note that other groups have spent a great deal of time working on “Delmarva Conservation
Corridors” and that individuals interested in wildlife travel corridors and habitat fragmentation
should contact the U.S. Fish and Wildlife Service’s Delaware Bay Estuary Project Office for
information on these corridors (302-653-9152).
54
Conclusions
The findings of this report should be considered preliminary. Field checking should be
conducted to validate the interpretations. The report should, however, serve as a guide to
wetlands in the Nanticoke watershed and to their functions. It is a starting point for resource
planning rather than an endpoint. The characterization serves as one tool to aid in wetland
conservation and watershed management. It should be used with other tools derived from field
observations and other site-specific data.
In the final analysis, a few issues arose that warrant further consideration by the State’s ad hoc
committee for the Nanticoke. These issues are mostly related to the criteria used for identifying
wetlands of potential significance for some functions. For streamflow maintenance, should
ditched portions of headwater wetlands be given the same rating as nonditched portions? In our
assessment, the former were identified as having some potential for this function, while the latter
were designated as having high potential. Should all floodplain wetlands be designated as having
potential for streamflow maintenance or should this potential only be attributed to floodplain
wetlands along low order streams and not to those along mainstem rivers? For nutrient
transformation, based on field investigations, is there a reliable positive correlation between
seasonally flooded and wetter water regimes and amount of organic matter in the soil? Also,
what is the role of seasonally saturated wetlands (“B” water regime; flatwoods) in nutrient
cycling? Presently, only those flatwoods with more than 50 percent of their borders in cropland
were deemed of some significance for nutrient cycling. For shoreline stabilization, pond-fringe
wetlands were included as having high potential for shoreline stabilization. Should they be given
a lower rating? Field checking of seasonally flooded and seasonally flooded/saturated emergent
wetlands should be done to determine if they are marshes or wet meadows. If the former, they
will likely have higher potential as both fish and shellfish habitat and waterfowl habitat than they
were given in this report. Palustrine tidal scrub-shrub/emergent wetlands and tidal
forested/emergent wetlands were designated as having moderate significance for waterfowl and
waterbirds, should their status be upgraded to high potential? All vegetated wetlands were
identified as having at least some potential as habitat for other wildlife. Is the committee still
comfortable with this?
In regard to fragmentation, for this study, we focused on major road crossings and did not treat
small isolated pieces of once larger wetlands that have been chopped up by development as
fragmented. Would it be better to apply this modifier (“fg”) to all potentially fragmented
wetlands? While a four-lane highway (interstate) clearly represents a fragmenting structure, does
a two-lane paved road produce similar consequences? And if so, what about unpaved roads?
Another question arose in applying the fragmentation descriptor to wetland polygons - should
this descriptor be applied to: 1) the entire wetland (main wetland body and the fragmented
section), or 2) only to the fragmented piece(s)? Many large wetlands only had a small portion
that was fragmented.
55
Acknowledgments
This study was funded by the Delaware Department of Natural Resources and Environmental
Control (DNEC), Division of Soil and Water Conservation. Sharon Webb was the project
coordinator for DNREC. Ralph Tiner serving as principal investigator for the Service.
Photointerpretation of wetlands, potential wetland restoration sites, and land use/cover for this
project was performed by John Swords. Gary Doucett mapped the extent of ditches. Wetland
classification of HGM-types following Tiner (2000) was performed by Herb Bergquist who also
processed much of the geospatial data. Bobbi Jo McClain produced the thematic maps and
assisted in data tabulation. Ralph Tiner developed the correlations between wetland
characteristics and wetland functions used to produce the preliminary assessment of wetland
functions, analyzed the data, and prepared the project report. Susan Essig reviewed the final
manuscript for clarity and content.
Amy Jacobs (DNREC) and the wetland group she assembled for reviewed the draft protocols for
correlating wetland characteristics with wetland functions and provided recommendations to
modify the selection criteria. Participants included David Bleil, Katheleen Freeman, Cathy
Wazniak, Mitch Keiler, and Bill Jenkins (Maryland Department of Natural Resource); Julie
LaBranche (Maryland Department of the Environment); Marcia Snyder, Dennis Whigham, and
Don Weller (Smithsonian Environmental Research Center); Matt Perry and Jon Willow (U.S.
Geological Survey); Mark Biddle (DNREC); and Peter Bowman (Delaware Natural Heritage
Program). Mark also provided land use and land cover information from the state’s digital
database. Peggy Emslie (formerly with DNREC) helped initiate this project by identifying the
value of this type of analysis for watershed planning and management.
56
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